BIUCHIOPODA. 



387 



SJiell smootH or radiately striated ; umbo of dorsal valve sub- 

 central ; of ventral valve sub-central, marginal, or prominent 

 and cap-like, with an obscui'O triangular area traversed by a 

 central line. 



The large muscular impressions of the attached valve are 



Fig. 193. Ventral valve. Fig. 194. Dorsal valve. 



Crcmia anomala, MuUer. ^ Zetland, 

 n, anterior adductors; a', posterior adductors; c, posterior adjustors ; c', cardinal 

 muscle ; r, o, central and external adjustors. 



sometimes convex, in other species deeply excavated ; those of 

 the upper valve are usually convex, but in C. Pari sien sis the 

 anterior (central) pair are developed as prominent diverging 

 apophyses. In C. tripartita , Miinster, the nasal process divides 

 the fixed valve into three cells.* 



C. Ignahergensis is equivalve, and either quite free or very 

 slightly attached. C. anomala is gregarious on rocks and stones 

 in deep water, both in the North Sea and Mediterranean (40 — 90 

 fathoms, living; 150 fathoms, dead; Forbes); the animal is 

 orange-coloured, and its labial arms are thick, fringed with 

 cirri, and disposed in a few horizontal gyrations (Fig. 195). 



Distribution, 5 species. Spitzbergen, Britain, Mediterranean, 

 India, New South Wales. — 150 fathoms. 



Fossil, 37 species. Lower Silurian — . Europe 



C. antiquissima, Eichw. (Pseudo-crania, M'Coy), is free, and 

 has the internal border of the valves smooth ; the branchial 

 impressions blend in front. SpondyJoholus craniolaris, M'Coy, 

 is a small and obscure fossil, from the Lower Silurian shale of 

 Builth. The upper valve appears to have been like Crania, the 

 lower to have had a small grooved beak, with blunt, tooth-like 

 processes at the hinge-line. 



* M. Quenstedt has placed the Oolitic Cranias in Si/Jionaria! 



s2 



