114 



A.B. SMITH ETAL. 



Fig. 23 Camera lucida drawings of plating in Stegaster cotteaui Seunes, 1 889, from the late Maastrichtian of Bidart (Pyrenees-Atlantiques, France); 

 BMUW 74603, a, oral surface; b, apical surface (interambulacra shaded). Scale bar = 5 mm. 



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 1 93 1 : 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 of Bidart, Pyrenees-Atlantiques, France. 1-3, BMUW 74603, oral, lateral and apical 



views, xl. 4, 5, BMUW 94985, oral and lateral views, xl. 

 Figs 6-8 Tholaster munieri (Seunes, 1889), BMUW 94993, Upper Maastrichtian of Bidart, Pyrenees- Adantiques, France. Apical, oral and lateral views, 



xl. 



