122 



BRACHIOPODA. 



the dorsal valve and two corresponding sinuses on the 

 ventral. Hinge-line curved. Umbone of ventral valve 

 truncated by a circular foramen, having a deltidium 

 at its base. Brachial skeleton in the form of a short loop 

 extending to only about a third of the length of the shell. 

 Devonian to present day. 



Waldheimia (fig. 32). Distinguished from Terebra- 

 tula by the longer brachial loop, extending to at least 

 half the length of the shell, and by a median septum in the 

 dorsal valve, which is however sometimes rudimentary. 

 Lias to present day. 



Stringocephalus (fig. 43). Shell nearly circular in 

 outline ; smooth. Ventral valve with a sharp prominent 

 umbone, area present. Foramen large and triangular in 

 the young individuals, smaller and oval in the adult on 

 account of the development of the deltidium. Teeth 

 large. Ventral valve with a median septum (vs), which 



A B 



FIG. 43. Stringocephalus burtini, Devonian. A, Dorsal valve. B, Profile. 

 a, adductor; c, crura; I, loop; j, cardinal process; p, hinge-plate; 

 s, dorsal septum ; vs, ventral septum ; t, dental sockets. (From 

 Woodward.) 



