'284 DE. C. T. TEECHMAFIS^ O'S [vol. IxXlii, 



The following account of the internal structure is based chiefl}'' 

 on large specimens of Hectoria tumid a, from the Rhaetic of 

 Benmore Cutting, where fine moulds and casts occur, from which I 

 obtained gutta-percha impressions. The interior of the ventral 

 valve is considerably thickened posteriorly by deposition of 

 shelly matter; the hinge-teeth are prominent, are supported by 

 short dental plates, and there is a short median septum. 



In the dorsal valve the hinge-region is still more thickened; 

 the cardinal process is very large and prominent, and consists of a 

 blunt tongue-shaped mass of shell, which projects backwards 

 beneath the delthyrial region of the ventral valve. The cardinal 

 process has a shallow depression on its surface. In front of the 

 ■cardinal process a deepened cavity projects backwards beneath it, 



IFig. 5. — Gutta-percha squeezes of interior of apices of valves of 

 Hectoria tumida, gen. et sj). no v. (JSfatural size.) Rlicetic. 

 Benmore Cutting. 



<i^»!|%fc 



^r^ 



a = Dorsal valve, showing the large tongiie-like cardinal process with the 

 hollowed-out space in front of and beloAv it divided by a median septum. 

 Slight dental sockets occur on each side of the cardinal process. 



b=yentral valve, showing the concave slightly-striated area, the small 

 hinge-teeth and plates supporting them, and the small median septum. 



and is divided hj a rather high, blunt, median septum which 

 separates the two adductor-scars. On each side of the cardinal 

 process is a fairly-deep dental socket. The ovarian pittings, 

 vascular impressions, and muscle-scars are well marked in both 

 valves, the diductor-scars of the ventral valve being flabellate. 

 The spiral cones are lateral^ directed. The arrangement of the 

 juga and junction of the spiralia with the crura could not easily be 

 seen ; but, on grinding down a specimen from the Carnic shales 

 at Otamita, I concluded that it was similar to that which obtains 

 in other Spirigerids. 



