BTIACHIOPODA. 



387 



Shell smooth or radiately striated ; umbo of dorsal valve sub- 

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

 and cap-like, "with an obscure triangular area traversed by a 

 central line. 



The large muscular impressions of the attached valve are 



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



Crania anomala, MuUer. ^ Zetland. 

 a, 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. Parisiensis 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). 



Distrihution, 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 ujiper 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 Siphonaria 1 



s2 



