BRACHIOPODA. 



331 



convex on both sides; dorsal valve with a short truncated 

 beak, with a foramen at the extremity, which is entirely 

 enclosed by the continuous edge of the shell, but without 

 any deltidium, or true area ; hinge with two strong teeth 

 in the dorsal, fitting into sockets in the ventral valve; 

 on the dorsal valve there are also two deep grooves reach- 

 ing from the beak to near the middle of the shell, which 

 receive two strong diverging teeth placed on the opposite 

 valve ; this system of articulation gives great thickness to 

 the interior part of the shell ; ventral valve with a medial 

 ridge from which rise a pair of arched calcareous plates. 



The only species is B. [ Terebratula'] rosea of Sowerby, 

 from Brazil. 



Terebratula. UOrb. — Shell free, of a punctured 

 texture, oval or round, depressed or gibbose, inequivalve ; 

 the upper valve larger, convex, with no dis- 

 tinct area, but a projecting beak, obliquely 

 truncated ; lower valve smaller and less gib- 

 bose with its arched summit concealed under 

 the deltidium of the upper valve; opening 

 round and terminal, at the extremity of the 

 beak of the upper valve, and separated from 

 the lower valve by a deltidium formed of the Terebratula. 

 pieces soldered together. Internal apparatus 

 on the lower valve formed of lateral callosities at the 

 hinge supporting two cartilaginous, or testaceous arms 

 which fold back and meet. — 1 species ; also fossil. 



This genus by D'Orbigny admits only those species 

 which have a round hole in the point of the boss of the 

 dorsal valve, which therefore appears blunt ; the area is 

 wanting ; but a distinct deltidium exists. T. cranium is 

 the living species, found on the coasts of Norway. Fossil 

 species are in great numbers, from the oldest to the newest 

 formations. 



