A revision of mid-Cretaceous textularian foraminifers from Texas

As Cretaceous species previously placed in Bigenerina, Siphotextularia, and Textularia differ from typical Cenozoic representatives of these genera in having solid non-canaliculate walls, 16 species from the Fredericksburg and Washita Groups (Albian-Cenomanian) of Texas and Oklahoma have been restudied. The new genera Heterantyx with type species H. antonovae sp. nov. and Quasispiroplectammina with type species Spiroplectammina longa are assigned to the family Spiroplectamminidae. A new family Textulariopsidae is proposed for basically biserial taxa with solid walls and includes Plectinella, Textulariopsis, of which two species T. lechriosa and T. texhomensis are new, the reinstated genus Bimonilina, with a new species B. reciprocata, and three new genera, Aaptoioichus, Haimasiella and Minyaichme.


INTRODUCTION
The presence of perforated or canaliculate walls in agglutinated foraminifera has been sporadically observed but taxonomically neglected. Study of Recent and other Cenozoic species by various workers (Hofker, 195 1, 1976;Coleman, 1980;Banner & Pereira, 1981) suggests that a greater emphasis should be placed on such wall characters. Thus, Banner & Pereira (1981) transferred from Textularia the Cretaceous taxa with solid walls, and regarded these as a new genus Textulariopsis which they placed in the subfamily Verneuilininae, family Ataxophragmiidae.
In working on a foraminifera1 suprageneric reclassification, we have reexamined certain mid-Cretaceous assemblages from the American Gulf Coast that we had studied earlier, including species originally described as Bigenerina, Siphotextularia, Spiroplectamrnina, and Tt9xtularia. Most of the species were originally described in the 1930's and 1940's, hence solely o n the basis of light microscopy. A s most are relatively tiny species, details of wall character were not evident. For the present paper we have restudied these species and a few additional new species, and have examined half-sectioned specimens in the scanning electron microscope (SEM) to determine the character of their walls.

METHODS
In addition t o study and camera-lucida illustration of these species with the light microscope, half sections were prepared of each species with the method described by Hofker (1933) and Coleman (1979). Specimens embedded in paraffin were ground on a 600 size carborundum sheet using castor oil as a lubricant; after pdishing and removal of the paraffin in xylene, specimens were mounted on plugs for SEM examination.
All were found to have solid, noncanaliculate walls, although this is not surprising in view of their very thin walls and generally small size. Atlantic Deep Sea Core A 167-25, a 17Scm core at a water depth of 1745m from the Blake escarpment, at 28"52'N. Lat., 76'47'W. Long. This material was dated by A.R. Loeblich, Jr. iis Cenomanian, and slightly younger than the surface Washita Group of Texas and Oklahoma (Ericson et al. 1961, p. 236).
All types and figured specimens are deposited in the U . S . Nation a 1 Muse um , Washington , D . C.  5) fro in the Georgetown For m a t io n in a ' 'Gryp hueu ' ' agglomerate at a concrete ford. 1.8m. above base exposed. locality 96. Paratype (figs. I , 2) and unfigured paratypes from the Goodland Formation in a massive chalky limestone about 1 3 m below top of exposure at locality 248. Other specimens were studied from the Good 1 and . Georgetown a 11 d Dent on Form at ions .

Description.
Test free, with a lozenge-shaped crosssection having the margins truncated and the angles with prominent ridges, early chambers in a small planispiral coil. commonly with four chambers surrounding the proloculus before the first pair o f biserial chambers, biserial chambers increasing gradually in size a s added; sutures straight, strongly limbate and elevated. zigzag suture forms a median ridge, more elevated than the lateral sutures. extending from just above the proloculus t o die out just helow the final two pairs of biserial chambers; wall very finely agglutinated, surface finely granular in appearance in the optical microscope; aperture a low slit at the base o f the last formed chamber.  . but differs in having ;I more prominent and elevated zigzag suture that extends upward from just above the planispiral coil t o disappear on the final two pair of biserial chambers. T h e Texas \peeics is slightly larger, its the maximum measurements of the Russian species are 0.45mm length, 0.50 width. and 0.22mm in thickness. H . utztonovue differs from H . rc,c~/ringuluris (ten Dam) and H . crciosu (ten Dam) in having fewer chambers i n the early coil (fivc instend o f 8-Y) and i n enlarging more rapidly with growth. i n the lozenge-shaped cross-section. truncate margins and the straight and prominent median ridge terminating just hclo\v the last two pair o f chambers.

Diagnosis.
Genus o f Spiroplectarnminidae that shows a growth pattern of gradual chamber size increase. producing ;I test that is intermediate i n form between Spirop1t~crr1mminrr and Spirorutilis ~ a sm all coiled s tsge being followed by ;I later gradually enlarging biserial stage with an ovate or rarely circular cross-section. Description. Test free, increasing gradually in size. the ciirly planispiral coil bcing smaller thaii the succeeding hisetid stage. and in the same plane its the biserid chambers; test oval t o broadly ovate in section o r ovate to nearly circular depending on growth pattern; wall thin, very finely agglutinated. t o almost appear hyaline, o f caIc:treoii\ t o siliceous particles. t a t disintegratcs i n 11CI. half-sections i n S E M show the wall t o be solid and noncan~tlieul~tte; aperture ii low arch at the base of the lm t f o rmed cham be r . Remarks. ~ur~si.spiropl~~c.turrlrninu gen. nov. differs from .Spir[)pl~J~t~irnminri in having an early coil that is o f lesser dia me te r t h ;t n the following gradually e nl ii rg i ng bise rial portioii, whereas in SpiroplectumminlIi the coil is larser. &uu.si.spiroplcctummir~rr is soluble i n HCI a s is the type \pecies o f Spiroplc~c~trimmirzu although some fossil species o f the latter are insoluble. I t differs from Spiroriitilis in having an oval t o circular cross-section rather than bcing flattened t o diamond-shaped in section.
~uasi.spiroplrc~trrnirnirzu mlrx-undrri (Lalicke r, 1 9 35) (PI.  (Lalickcr, 1935) (PI.  Remarks. Spiroplectumrninu was restricted by Hofker (1976) and redefined by Banner & Pereira (1981) t o include o n l y those species with solid wall. lacking canaliculi arid pseudopores, with large initial planispiral coil followed by a biserial stage o f lesser width than the coil, and an uncompressed test with ovoid cross-section. Some species previously included in Spiroplrc~tutnminu were transferred t o Spirorutilis Hofker. which has ;I biserial stagc broader than the early coil, and ;I laterally compressed test commonly rhombic in section and. in the type species. with ;I sharply angled t o subcarinate periphery. True Spiroplec~tumminu is present in the Texas mid Cretaceous. ;IS well a s those species we have t ra ncfe rred t o Quu.sispirop/rc~tamrnirzu ge n .  (Tappan. 1943) and also occurs in the Weno, Paw Paw, Grayson and Del Rio Formations elsewherc in Oklahoma and Texas. Remarks. S. ammovitreu is a true Spiroplectamminu, with large initial planispire, followed by nearly parallel sided narrow biserial portion and with ;I solid, noncanaliculate wall as seen in SEM observation o f half sectioned specimens. I t is insoluble in HCI.
Family Textulariopsidae fam. n o v . Type genus. Trxtuluriopsis Banner 6i Pereira, 198 1 . Diagnosis. Free-livi ng foraminifers with early bise rial stage, o r may have a ainglc adventitious chamber producing a pseudotriserial base; later stage may be hiserial. loosely biserial or uniscrial; wall agglutinated. sol id and n o 11 can a 1 i cu 1 ate . Description. Test free, early stage biserial, o r with a single adventitious chamber resulting in a pseudotriserial arrangement at the base. later biserial stage may be slightly twisted, final stage may become loosely biserial o r completely uniserial; aperture in the biserial stage an arch at the base o f the final chamber, and may become slit-like in the face, to terminal in the final stage. Wall agglutinated, solid and noncanaliculate, may consist of calcareous or siliceous particles, held in a calcareous cement (disintegrating in HCI) or held in an organic cement and insoluble in HCI (Aaptotoichus). Horizon. As far as known, the family occurs from Lower Jurassic (Pliensbachian) to Upper Cretaceous (Maastrichtian). Remarks. The genera Textulariopsis and Plectinella were placed in the subfamily Verneuilininae of the family Ataxophragmiidae by Banner & Pereira (1981), on the basis of the solid, noncanaliculate wall, in contrast to the Textulariidae, which appear to be largely Cenozoic in age and to have a canaliculate agglutinated wall. The group of genera here placed in the Textulariopsidae differ from the Ataxophragmiidae in being biserial in the early stage, or with a single adventitious third chamber at the base, rather than having a distinct early triserial stage (Verneuilininae) or distinct early spire (Dorothiinae, Ataxophragmiinae). Six genera are here included: Bimonilina Eicher, 1960

Derivation of name.
Greek aaptos, invincible + toichos, wall of house. Gender masculinc. Diagnosis. Test with short early biserial stage followed by a longer uniserial portion of broad low chambers, commonly compressed in preservation. Wall agglutinated, solid, without perforations, but thin and commonly deformed, insoluble in acid. Aperture terminal, rounded. Description. Test tiny, short biserial stage of rapidly enlarging broad low chambers followed by uniserially arranged chambers that are round in cross-section, but commonly compressed in preservation, and increase only slightly in diameter. Wall agglutinated, insoluble in HCI, consisting of fine siliceous particles, solid and noncanaliculate. Aperture becoming terminal in the uniserial portion, small and rounded. Remarks. A aptotoichus differs from Bigenerina in having solid noncanaliculate walls, and in the smaller size (about 1/3 that of the type species). It differs from both Bigenerina and Haimasiella gen. nov. in having a wall of organic material with siliceous particles, and is insoluble in HCI.
In addition to the type species, Ammobaculoides pitmani Crespin = Bigenerina pitmani (Crespin) Haig, from the Aptian and Albian of Queensland and South Australia may belong to Aaptotoichus; the specimens referred to Bigenerina clavellata by Bartenstein & Brand (1951, pl. 4, figs. 75, 76), although not this species, certainly do belong to Aaptotoichus. The genus ranges from Valanginian to early Cenomanian in age.
Aaptotoichus clavellatus (Loeblich & Tappan, 1946) (PI. Description. Test free, small, elongate, biserial throughout, loosely so in the later stages, slightly twisted during growth, each new chamber formed overlaps both of the preceding biserial pair and appears to be a terminal uniserial chamber, rarely a terminal chamber touches only one of the preceding pair; chambers inflated, increase slowly in width, but rapidly in height; sutures depressed, wall thin, finely agglutinated, rather smoothly finished; aperture an elongate slit, areal in position and terminal on the final chamber. Dimensions. Holotype 0.38mm in length, 0.16mm max. width, 0. lOmm thickness; paratypes 0.35 mm in length, 0.14mm in width, 0.13 mm in thickness and 0.23mm in length, 0.08mm in width and 0.06 in thickness. Remarks. B . reciprocata sp. nov. differs from B . variana Eicher in being more compact and in being less tapering, less compressed and in tending more toward a truly uniserial development. Genus Haimasiella gen. nov. Type species. Haimasiella wintoni (Cushman & Alexander) = B i g e n e r i n a w i n t o n i Cushman & Alexander, 1930. Derivation of name. Greek Haimasiella wintoni (Cushman & Alexander, 1930) (  fig. 6, hypotype, Weno Formation, locality 47; fig. 7, hypotype, Paw Paw Formation, locality 40. Note short, rapidly expanding biserial portion with inflated chambers, followed by uniserial stage of nearly constant breadth and short inflated chambers. (All x63.)   (Tappan) = Siphotextularia subcretacea Tappan 1943.

Derivation of name.
Greek, minys, small + aichme, point of a spear, with reference to the general test shape. Gender feminine. Diagnosis. Test free, elongate, consisting of biserially arranged chambers enlarging gradually as added, rarely with a third adventitious chamber at the base giving a pseudotriserial appearance, sides flattened, angles rounded to acutely angled, commonly forming ridges that arise near the base. Wall solid, noncanaliculate, dissolves rapidly in HCI. Aperture large, ovate, areal, subterminal to terminal in position. Description. Test free, elongate, sides of test flattened to concave with angled to subrounded edges that may become prominent ridges at the four angles, relatively few chambers, biserially arranged and enlarging gradually as added, sutures nearly horizontal, only slightly depressed. Wall solid, noncanaliculate, thin, of whitish calcareous particles cemented together; aperture ovate, areal, subterminal to terminal on the final chamber. Remarks. Species now referred to Minyaichme gen. nov., were previously placed in Siphotextularia or Textularia, but both of the latter genera are Cenozoic ones with canaliculate walls. In addition, the aperture of Minyaichme is areal and subterminal rather than at the base of the final chamber as in Textulariu and is not produced on a neck as in Siphotextularia. ('Tappan, 1943) (PI. 2, figs. 16-19) 1943 Textularia duckcreekensis Tappan:486,pl 18,19) and additional specimens from the Georgetown Formation, from a 1 m section just beneath a zone of numerous "Gryphaea" washitensis, about 1.5km downstream from road at locality 96. The species was originally described from the Duck Creek Formation in Grayson County, Texas. Remarks. The species was originally referred to Textularia because of the biserial chamber arrangement, but the aperture was stated (Tappan, 1943, p. 486) to be "slightly elongate, apparently in the face of the lastformed chamber, rather than at its base." Both the character of the aperture and the solid rather than canaliculate wall, as indicated by SEM study of half-figs. 10a-c.

Minyaichme duckcreekensis
sectioned specimens, show this species to be generically distinct from Textularia. It differs from M . subcretacea (Tappan) in being more elongate, tapering, and flattened and in lacking the four distinct ridges at the angles of the test.
Minyaichme subcretacea (Tappan, 1943) (Pl. 2, figs. 29-31) 1943 Siphotextularia subcretacea Tappan:486,pl Remarks. This species is typically biserial throughout but occasional specimens may have a third adventitious chamber at the base that gives a pseudotriserial appearance. Because of the biserial chamber arrangement and areal aperture this species was originally placed in Siphotextularia. However, Siphotextularia has a canaliculate wall, and the aperture is produced on a neck unlike the present species. The wall of the present species is solid and noncanaliculate as seen in SEM examination of half-sectioned specimens. The wall is thin, whitish in appearance and readily soluble in HCI. The sharp angles at the four corners of the test sides give a distinctive appearance to this species.
Genus Textulariopsis Banner & Pereira, 19811981 Textulariopsis Banner & Pereira:98. Type species. Textulariopsis portsdownensi.s Banner & Pereira 1981. Remarks. Banner & Pereira (1981) studied the wall structure of a variety of agglutinated species, and found that certain Cretaceous species previously referred to Textularia have a solid wall whereas typical Textularia has a canaliculate wall. They proposed the new genus Textulariopsis for those with solid walls, regarding these as closer to the Mesozoic Ataxophragmiidae than to the Cenozoic Textulariidae. Three Texas Lower Cretaceous species previously referred to Textulariiz are here transferred to Textulariopsis, and two new species are described. In addition to these Cretaceous taxa, Textularia areoplecta Tappan, 1955 from the Lower Jurassic (Pliensbachian-Toarcian) of northern Alaska is here transferred as Textulariopsis areoplecta (Tappan). Remarks. This species is similar to Textularia hybrida Chapman, 1899 but is about one half as large, increases more rapidly in width, and also increases slowly in thickness rather than being of identical thickness throughout.

Textulariopsis Iechriosa
Textulariopsis losangica (Loeblich & Tappan,195  Remarks. This species is characterized by an angular periphery and raised zigzag suture between the two series of chambers, resulting in a diamond-shaped crosssection. The test may flare rapidly in the early stage, but in the very large specimens the later stage may have nearly parallel sides, the chambers increasing little if any in size as added. The wall is solid, noncanaliculate and of agglutinated calcareous material completely disintegrating in HCI. (Carsey, 1926) (PI. 2, figs. 26-28) 1926 Textularia rioensis Carsey:24,pl. 7,fig. 12. Material. Several thousand specimens. Locality and horizon. Figured hypotype (figs. 26,27) from the Goodland Formation in a 90cm section of yellow grey marl, about 30cm above the road level at locality 73. Figured hypotype (fig. 28) from the Fort Worth Formation in a 90cm section of marl between heavy limestone beds, 3m above the base of the exposure at locality 56. Other specimens are from the Walnut, Goodland, Kiamichi, Duck Creek, Fort Worth, Denton, Weno, Paw Paw, Main Street, Grayson, Georgetown, Del Rio and Maness Formations. It also has been reported from the Glen Rose Formation of the Trinity Group in Texas. Remarks. One of the most abundant species of Textulariopsis in the Gulf Coast mid Cretaceous, this species has a solid noncanaliculate wall as viewed in half-section in the SEM. It is agglutinated of calcareous particles and dissolves rapidly in HCI.
(PI. 2, figs. 38, 39) Derivation of name. With reference to the type locality of the species, from the cxcavation of the Denison Dam of the Red River which now forms Lake Texhoma at the boundary between Oklahoma and Texas. Diagnosis. A species of Textulariopsis with an elongate. narrow, tapering test with chambers of early part little inflated and sutures flush with the surface, but chambers o f later part intlated and sutures depressed.
Holotype. Specimen o f PI. 2, figs. 38, 39. Material. Over 200 specimens. Locality and horizon. Holotype from the Duck Creek Formation from a 1 . 6 m section o f blue and yellow clays just beneath a heavy limestone bed, 2.5m below top of cxcavation, and 17.6m above the basal contact with the Kiamichi Formation at locality 104. Unfigured spccim e m are from the Duck Creek and Fort Worth Formations. Description. Test free, elongate, narrow, biserial throughout or with a single adventitious chamber at the base appearing pseudotriserial, test increasing slowly in width with growth, rarely the test is twisted somewhat in the upper third, chambers with little o r no inflation in carly portion, with sutures flush with surface and directed very slightly downward toward the outer edge, later chambers inflated with sutures nearly horizontal and depressed; wall coarsely t o finely agglutinated, o f calcareous particles that dissolve in HC1, wall solid; aperturc a broad low arch at the base of the final chamber, occupying about half the width o f thc chamber facc. Dimensions. Holotype, length 0.86mm, width 0.28mm. thickness 0.24mm. Paratypes 0.22 t o 1.03mm long. 0. 1 1 to 0.33mm wide. Remarks. This species differs from TcJxtulariu influtu Gauger 1953 in tapering more rapidly, and in having a longer and thicker test. I t differs from Trxtufariu topagorukensis Tappan 1957 in being twice as large, and in its more inflated and more rounded cross-section. The wall is seen to be solid and noncanaliculate when half sectioned specimens are viewed in the SEM.
Textulariopsis wushitensis (Carsey, 1926) (PI. 2, figs. 32-37) I926 Textuluria washitensis Carsey:34, pl. 7. fig. 6 Remarks. This large species is common in the upper part of the Washita Group. The wall is agglutinated of calcareous particles and dissolves in HCI. Half sectioned specimens viewed under the SEM are seen to have a solid noncanaliculate wall as in other Textuluriopsis. Occasional specimens have a tiny adventitious chamber at one side of the proloculus, giving the superficial appearance of a single triserial whorl, or even a pseudocoil. From the opposite side the true biserial nature is apparent.