New Calcareous Nannofossil taxa from the Jurassic

Four biostratigraphically significant new calcareous nannofossil species are described, Biscutum davyi, Lotharingius contractus, Lotharingius velatus and Retecapsa incompta, together with three new combinations.


TAXONOMY
The new taxa are presented as type series (holotype + isotypes) described and illustrated via scanning electron and light microscopes. It is considered expedient to utilize both these viewing techniques in the description and illustration of new nannofossil taxa (preferably using same specimen techniques, e.g. Gallagher, 1988). Together they provide the optimum amount of information concerning crystallographic construction, gross surface morphology and ultrastructure, thus promoting accurate, unambiguous description and logical, consistent classification. Holotypes and isotypes are quoted as film and frame numbers which are-housed in the Postgraduate Unit of Micropalaeontology, Department of Geological Sciences, University College London. Holotype dimensions are given in brackets. Taxonomic references not given in the reference list may be obtained from Bown, 1987, andGrun andZweili, 1980. Remarks. The species name sexirudiatus Pienaar, 1969 is considered a junior synonym. The genus Corollithion Stradner 1961 was defined to include coccoliths with hexagonal outlines and is thus not suitable for the inclusion of this species. The generic concept of Stradnerlithus given in Perch-Nielsen (1985) allows the

Remarks.
A broad generic concept of Stradnerlithus, e.g. Perch-Nielsen (1985), allows the inclusion of this species. The elements of the distal shield are joined along radial sutures, with some kinking near the inner edge of the outer cycle (veeing in an anticlockwise direction). The proximal shield is considerably smaller than the distal shield, to which it is closely adpressed, and is formed from a broad cycle of non-imbricating, radial elements. At its inner edge the proximal cycle appears to interlock with a narrow second cycle which is thought to represent the base of the cycle described on the distal side as the inner distal cycle. The central area is small and almost completely filled by a cross structure made up of a prominent longitudinal bar, broad at its centre (where there is a small central process) and tapering towards its ends (running parallel to the central area edge); subsidiary transverse components complete the central complex (PI. 1, fig. 17). In the light microscope (crossed-polars) the outer part of the shields is relatively dark but the inner cycle is distinctly bright. The cross bars are bright in certain orientations.

Dimensions.
Distal shield length: 5.2-6.2 (5.8)p.m width: 4.3-5.2 (5.0)pm Proximal shield length: 3.2-4.0p.m width: 3.0-3.3p.m Remarks. Biscutum davyi is a distinctive species which has only been recorded from the type locality where it has a restricted stratigraphical range in the falciferum Zone (Lower Toarcian). It is one of a relatively large number of species which diversified from the Biscutum  fig. 22). Isotypes. UCL-2622-3 (PI. 1, fig. 23), UCL-2622-7 (PI. 1, fig. 24), UCL-2668-32 (PI. 1, figs. 26). Type locality. Brenha, Portugal. Type level. Aalenian. Description. A relatively small coccolith possessing a typical retecapsid rim type (i.e. distal shield horizontal or inward sloping; radiating, non-imbricating rim elements; at least two distal rim cycles including the diagnostic narrow outer cycle). The distal shield has two cycles, a broad inner cycle and a narrower, peripheral outer cycle. The inner and outer cycles are formed from 20-30 non-imbricating elements joined along radial sutures. The structural relationship between these two cycles is uncertain but proximal and side views appear to show the inner cycle lying over the outer cycle and thus revealing only a narrow outer part. The proximal cycle is unicyclic and formed from non-imbricating elements joined along radial sutures which kink near their inner edge, veeing in an anticlockwise direction. The central area is spanned by a cross structure which supports a central spine. The cross bars are oriented along the principal axes of the ellipse and are composed of elongate elements aligned along the bar's length. On the proximal side the bars have median furrows which run into a central pore, marking the position of the spine. In the light microscope (crossed-polars) the broad inner cycle is bright and the narrow outer cycle is dark. When aligned along the polarising directions the cross bars are bright with dark median lines. The bars taper towards their outer edge.
Dimensions. Length: 5 .O-5.9 (5.7) p m Width: 3.6-4.4 (4.2)pm Remarks. This species does not fit readily into any genus (due to overly restrictive generic diagnoses in this family), however, its affinities clearly lie with species of the genus Retecapsa, i.e. retecapsid rim and prominent cross-bars. The lack of additional small lateral bars (a diagnostic character) is not considered significant enough to warrant the formation of a new genus. The evolutionary proximity of this earliest species of Retecapsa to, for example, Retecapsa schizobrachiata (Gartner, 1968) Grun in Grun and Allemann, 1975 (which possesses cross bars together with 8 small lateral bars) is quite evident. Other genera of the Retecapsaceae, e.g. Polypodorhabdus and Cretarhabdus, are not appropriate as they possess more complicated central structures with multiple lateral bars and grills. R. incompta is biostratigraphically significant, appearing in the latest Toarcian (levesquei Zone) after a period with few or no nannofossil appearances. It is also evolutionarily important, possessing the first retecapsid rim and representing the earliest member of the subsequently diverse Retecapsaceae. Type locality. Brenha, Portugal. Type level. Aalenian. Description. A relatively large, broadly elliptical coccolith with a watznauerian rim structure (see Bown, 1987, p.66 for full description of rim). The central area is small and almost completely filled by cross bars orientated with the principal axes of the ellipse and a central process which may represent a spine base. A number of specimens show additional lateral bars filling the small quadrants left by the principal cross bars. Dimensions: Rim length: 5.7-7.5 (7.2)p-n width: 4.8-6.9 (6.0)pm Remarks. Lotharingius contractus has a first occurrence, in northern Europe. in the rnurchisonae Zone (Aalenian) and represents a significant biohorizon. The species is an intermediate form between typical Lotharingius species (e.g. L. sigillatus (Stradner. 1961) Prins in Grun et al. 1974, L. crucicentralis (Medd, 1971) Grun and Zweili, 1980) 1, fig. 8).
Explanation of Plate 1 c-p = cross-polars, p-c = phase contrast. Figs. 1-3 Bown, 1987, p.66). The wide central area is clearly delineated and filled by a granular plate. The plate may be formed from relatively equidimensional grains or have a longitudinal component formed from coarser grains with finer grains around the edge of the central area; perforations may exist at the junction between these two grain types (PI. 1, fig. 10). In the light microscope (crossed-polars) the rim is characteristically bright with four curving isogyres. The central area is filled by a plate which appears slightly darker than the rim. The plate appears to be homogenous in structure but in certain orientations four dark isogyres form a cross approximately parallel to the principal axes of the elliptical centre (PI. 1, figs. 13, 15). There is some indication of a cross-like basis to the structure. Dimensions: Length: 5.7-6.8 (6.0) p m Width: 4.5-5.6 (4.8)pm Remarks. This species is placed in the genus Lotharingius as its ellipticity, size, rim structure and central area form are identical to that seen in Lotharingius sigillatus and L. crucicentralis. In addition, the central plate also shows signs of an antecedent and diagnostic Lotharingius central cross structure. A morphological development comprising infilling of the central bars to form an has arisen over the naming of these common watznauerian coccoliths, which possess a relatively small and vacant central area. The most appropriate valid name is fossacincta Black, 1971. The species is placed in Watznaueria, as Ellipsagelosphaera is considered to be a junior synonym of the former genus. Both generic names were introduced within a year of one another Noel, 1965) and applied to coccoliths with identical rim structures, and both included coccoliths with small, vacant central openings. The perpetuation of this division appears unnecessary.