Revision of the genus Valvobifarina Hofker, 1951 (Foraminiferida)

The genus Valvobifarina is exhaustively revised to include three species; V. mackinnonii (Millett), the type species, V. robusta (Sidebottom), and V. niobeae sp.nov. All species are typified. Bifarina elongata Millett, 1900 is excluded from Valvobifarina.


INTRODUCTION
The genus Valvohifarina is little known, perhaps because of its relative rareness and occurrence in more shallow water zones. Millett (1900) describedBifarina mackinnonii as being very rare in the Malay Archipelago, but he had seen some more specimens in gatherings from RaineIsland, the famous 'Challenger' Station 185, and from the Straits of Macassar. HeronAllen and Earland (1 91 5 ) found two specimens in the Kerimba Archipelago and a few in samples from Madagascar. They commented that the species had a wide distribution in shallow tropical waters.
The genus Valvohifarinu was created by Hofker in 1951. He apparently mistook V. mackinnonii for an arenaceous taxon, but described it correctly as lacking any indication of a toothplate. The new genus was classified in the Valvulinidae.
Loeblich & Tappan ( 1 964) classified Valvohifarina in the Pavonininae, close to Reussella. They supported Hofker's arguments that neither Loxostoma nor Valvohifarina are related to the bolvinids, the former having a granular wall and lacking a toothplate and Vulvobifurinu having a triserial, rather than a biserial early development. In the discussion of Bigenerina, they indicate that B . elongata Millett, 1900 ought to be removed to Valvohifarina.
In their latest classification, Loeblich & Tappan (1987) reinstated the Reussellidae, including Vulvohifarina in this family. No mention is made of the presence or absence of a toothplate.
The generic revision of the reussellid taxa showed that Valvobifarina amongst other genera, had to be removed from the Buliminacea to be reclassified in the Pavoninidae (Revets 1991 Description. Test free, elongate, early stage triangular in section, later stage laterally compressed, two first whorls triserial, last whorls twisted biserial to biserial; initial chambers rounded tetrahedral, outer edge may bear a small spine, biserial chambers large, cuneate, laterally compressed, outer edges prolonged into a distinct spine; sutures distinct, somewhat depressed, arcuate; aperture apical, slit-like, running along the upper edge of the chamber, bordered by a slightly everted lip; wall calcareous, hyaline, optically distinctly radial, perforate, pores large, at the apex of small mounds, arranged preferentially along the chamber edges. Remarks. The specimens described from Samoa by Cushman are lost vide Cushman, 1924, p.20).
Valvobifarina robusta (Sidebottom, 1918) 1918 Bifarina mackinnonii var. robusta Sidebottom: 125, pl. 3, figs 17, 18 1937 Bifarina mackinnoni var. robusta Sidebottom;Cushman: 201,pl. 23, fig. 8 Description. Test free, elongate, early stage irregular in section, later stages laterally compressed, biserial tending towards uniseriality; juvenile chambers rounded to subtetrahedral, rather low and small, adult chambers laterally compressed, cuneate, tending to become trapezoidal, upper edge somewhat arched, lateral edges crossing the peripheral edge, lowest edge of the chamber with a strong spine; sutures unclear, a depressed zone between the chambers; aperture apical, slit-like, running along the entire chamber length, bordered by a thickened and slightly everted lip, outer extremities pointed; wall calcareous, hyaline, optically distinctly radial, perforate, pores very large, at the apex of small mounds, few, arranged parallel to the long axis of the chambers, usually in one row plus a few scattered ones. Remarks.
The specimens described by Sidebottom (1918) from the 'Dart'Station 19, have been found in the collections of the British Museum of Natural History. All the specimens are located on anumber of faunal slides labelled 'Dart'. These contain besides figured specimens also a number of syntypes. Description. Test free, elongate, early stage rounded in section, later stage laterally compressed, at first triserial but soon reduced to twisted biserial; initial chambers obscured by thick secondary lamination, last 5 chambers subcuneate, laterally compressed, edges broadly rounded, lower ends not spinose and not crossing the edges of the test; sutures obscured, chambers not clearly delineated; aperture apical, slit-like, slightly twisted, running along the upper edge of the chamber, bordered by a thickened somewhat everted lip; wall calcareous, thickened by heavy secondary lamination, perforate, pores large, tending to crowd near the chamber borders. Remarks. This species differs from V . rnackinnonii in possessing much heavier secondary lamination which obscures the individual chambers, chambers which do not cross the periphery and do not bear any form of spinosity. The outer edges of the test and the individual chambers are also much more rounded. There is also a tendency in this species for the chambers not to embrace the previous aperture within their lumen, but to build the chamber on the apertural lip. Millett: 539, pl. 4, figs 1, 2 1937 Bifarina elongata Millett;Cushman: 200, pl. 22, fig. 35 1964 Valvobifarina elongata (Millett); Loeblich & Tappan: 654.

DISCUSSION
Valvobifarina poses some interesting questions concerning the way in which genera are related. Comparing the morphology of the species herein studied with some of the taxa treated earlier (Revets 1991), it has become more difficult to delineate the genera in question as sharply as has been the case until now. Valvobifarina mackinnonii is an archetypal example of Valvobifarina, but V . robusta can be seen as a step towards Bifarinella ryukyuensis Cushman & Hanzawa. Bifarinella in its turn could be one step away from Pavonina. The underlying trend lies not only in the gradual reduction of the amount and size of the triserially coiled chambers, but also in the increase in embracing of the biserialchambers. The relation between Valvobifarina and Bifarinella is more strongly pronounced when one takes into account that manyBifarinella specimens have at least some semicuneate chambers before building the typically reniform uniserial chambers.
The biogeographic distriubutions of this genus repeats the pattern found in Orrhoplecra (see Revets & Whittaker, 1991): there is a distinct clustering in the Malayan part of the Indo-Pacific Province, but specimens have been found in West Africa between Madagascar and the African continent (Fig. 1). This recurrent pattern cannot at present be explained, since the benthic genera found on both sides of the Indian Ocean do not seem to occur in the Indian or Arabian subprovince.

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Not enough information is at present available to venture any serious suggestions as to the evolutionary history of this enigmatic genus and its species