146 



sented in Leptoccelia (Jltrypa) planoconvexa, which has a some- 

 what undefined depression on the dorsal valve, and a form 

 of cardinal process unlike the other species. The internal 

 structure of this species is still unknown. 



The Leptoccelia imbricata proves to be a Trematospira, and 

 the same characters are apparent in L. dispariles of the Ni- 

 agara group, the concavo-convex form of the shell being 

 the only apparent deviation from typical forms of that 

 genus. The Terebratula lepida of Goldfuss, as shown in the 

 collections of Dr. Rominger possesses internal spires pre-i 

 cisely similar to those of Trematospira camura. 



The L. concava, both in its external characters and in the 

 arrangement of the crura and vinculum, differs from Tre- 

 matospira, and with the knowledge at present possessed, I 

 am compelled to separate this species from those last named, 

 and from the L. flabellites, L. jimbriata and L. acutiplicata, I 

 would propose to indicate forms of this external character 

 with similar crura and spires as Ccelospira. 



Fig. 37. 



Ccelospira Concava. 



The difficulty constantly attending the references of the 

 Brachiopoda, to established genera from external form and 

 characters, renders it very desirable to search for the inte- 

 rior organization and appendages ; but the condition of 

 specimens does not always admit of satisfactory investiga- 

 tions, 'and not unfrequently the specimens possessed are so 

 few as almost to preclude examinations of this kind. 



As an example of the diversity of internal structure in 

 similar external forms, I may mention the Terebratula alti- 



