344 TEREBRATULID^. 



the necessity for a revision of the Terehratula, and all that 

 has been done of late years on the subject, must be regarded 

 as fruit sprung from seed sown by him. In our country 

 his footsteps have been followed with varied success by 

 Phillips, Morris, M'Coy, and King. Their researches 

 have been mainly directed to the elucidation of the fossil 

 species. Very lately M. Alcide d'Orbigny has dii-ected 

 his sagacious mind to this important inquiry, and has 

 brought, with a bold hand, the work of his predecessors 

 and of himself, powerfully to bear upon both recent and 

 fossil forms. According to his view of the generic sec- 

 tions into which they should be divided, each of our 

 few British Terehratula would become a member of a 

 different genus, and even fall under distinct tribes. We 

 prefer regarding them as members of a single tribe, and 

 as forming part of three very distinct and easily re- 

 cognised genera. 



HYPOTHYRIS, Phillips. 



Shell tumid, thin, inequivalve, equilateral, its surface 

 marked with radiating strise or grooves, and never punc- 

 tated. Beak of upper valve entire, the perforation beneath 

 it triangular and open, reaching the margin. No cardinal 

 area. Apophyses consisting of two separate, curved, mo- 

 derately developed blades projecting from the hinge of the 

 lower or imperforate valve. 



Animal with spirally coiled buccal appendages or arms, 

 not fixed by a cartilaginous or testaceous skeleton. 



Only two existing forms of Terebratulce with non-punc- 

 tated shells are known, the one about to be described, 

 and the Terebratula nigricans of G. B. Sowerby, the 

 habitat of which is unknown. In the fossil state, how- 



I 



