No. 186.J 



31 



Genus Tropidoleptus ( Hall ). 



[ Gr. tQOTtig, carina; 7.£7trog, tenuis : the carinate ventral valve and 

 shallow visceral cavity, in its analogy with LEPTiENA.] 



Strophomena : CoNRAD. 



Leptcena : Hall, Owen, and others. 



Tropidoleptus : Hall, Regents' Report for 1856; Palaeozoic Fossils, 1857. 



Shell transversely oval or longitudinally semielliptical, one valve 

 convex and the other concave, articulating by teeth and sockets; 

 hinge-line equal to or less than the greatest width of the shell. 

 Ventral valve with a linear area and triangular foramen or notch 

 in the margin of the area : from the inner edges of this proceed 

 the dental lamellae, which are separated from the area by a nar- 

 row groove strongly crenulated on the outer edge and extending 

 obliquely outwards, terminating in a low ridge which partially 

 surrounds the muscular impression. Dorsal valve concave; the 

 cardinal process prominent, somewhat wedge-shaped, obtuse at 

 the outer extremity, and diverges in the interior, supporting the 

 bases of the crura. Dental fossets crenulate. 



Surface plicate : shell- structure punctate. 



The Strophomena carinata of Conrad is the type of this genus, and 



the only species determined at the present time (See Report of the Regents 



for 1856, page 111). 



Fig. 1 & 2. The exterior of the 

 ventral and dorsal valves of 

 a large individual. The ven- 

 tral valve is partially covered 

 by a bryozoum. 



Fig. 3. The interior of the ventral valve, showing the area^ foramen, teeth, etc., en- 

 larged. 



Fig. 4. The interior of the dorsal valve, showing the cardinal procees, the dental fos- 

 sets, the bases of the crura, and the septum. 



