. Bulletin of the Natural Histort Museum. Geology series. Fig. 23 Camera lucida drawings of plating in Stegaster cotteaui Seunes, 1889, from the late Maastrichtian of Bidart (Pyrenees-Atlantiques, France); BMUW 74603, a, oral surface; b, apical surface (interambulacra shaded). Scale bar = 5 Fig. 24 Camera lucida drawing of plating in Stegaster cotteaui Seunes, 1889, from the late Maastrichtian of Bidart (Pyrenees-Atlantiques, France); BMUW 74792, apical surface (interambulacra shaded). Scale bar = 5 mm. and its disjutict plastron distinguishes it from all but three species of Stegaster, S
. Bulletin of the Natural Histort Museum. Geology series. Fig. 23 Camera lucida drawings of plating in Stegaster cotteaui Seunes, 1889, from the late Maastrichtian of Bidart (Pyrenees-Atlantiques, France); BMUW 74603, a, oral surface; b, apical surface (interambulacra shaded). Scale bar = 5 Fig. 24 Camera lucida drawing of plating in Stegaster cotteaui Seunes, 1889, from the late Maastrichtian of Bidart (Pyrenees-Atlantiques, France); BMUW 74792, apical surface (interambulacra shaded). Scale bar = 5 mm. and its disjutict plastron distinguishes it from all but three species of Stegaster, S. cotteaui Seunes, S. chariest Lambert and 5. mairei Lambert, all Maastrichtian in age. In none of these are the latero- posterior interambulacra interupted as they are in our species. S. mairei fuither differs in being subglobular in shape with its periproct positioned much higher. S. cotteaui has a much narrower anterior sulcus, more anterior peristome (10% test length from the anterior rather than almost 30%) and is more depressed in profile. S. chariest resembles our species in profile, but, according to Lambert (1931: M7), has such a reduced labral plate that only ambulacral plates surrounding the peristome. Unfortunately the only plating diagram of 5. chariest (Lambert 1931: M5, fig. 3) gives insufficient detail and we have not examined Lambert's type to confirm this very unusual plate arrangement. Genus THOLASTER Seunes, 1891 Diagnosis. Test elongate with very deep frontal groove at ambitus and adorally; tapering to posterior truncation. Apical disc with four genital plates each with a gonopore. Aboral pore-pairs rudimentary, ambulacra flush. Frontal groove with sharp lateral carina; developed from apex to peristome. Oral surface flat. Plastron orthostemous. Periproct on posterior face. Very large primary tubercles prominent towards apex and along the aboral margins of the frontal groove. No fascicles. PLATE 6 Figs 1-5 Stegaster cotteaui Seunes, 1889, Upper Maastrichtian
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