44 



[Assembly 



Genus Teiplesia ( Hall, 1858 ). 



[ Grr. tQHTtlaaiog, triplex, in reference to the trilobate character of several 



of the species.] 



Shells transverse or elongate, trilobate or subtrilobate; the ventral 

 valve being marked by a broad deep sinuosity, and the dorsal 

 valve by a corresponding fold. Hinge-line straight : area small; 

 foramen triangular. External surface concentrically striated, and 

 with fine obscure or obsolete radiating strise : internal structure 

 not determined. 



I have proposed this name to include Atrypa extans, A. acspidata, and 

 A. nucleata of Vol. i, Palaeontology of New- York, as well as other species. 

 An examination of Atrypa extans has shown the existence of a narrow 

 area and small triangular foramen as in Spirifer; but I have not been able 

 thus far to determine the internal structure. The texture of the shell, and 

 surface marking, although differing in some particulars from those of Me- 

 rista, are nevertheless similar. 



Triplesia extans. 



Fig. 1. Yentral valve. Fig. 2. Dorsal valve. 



Fig. 3. Area and foramen of the 

 ventral valve. 



