S86 



irAXrAL OF THE MOLLTJSCA. 



Choxetes, Fischer. 



Example, C. striatella, PL XV., Fig. 29. 



Etymology, chone, a cup. 



Shell transversely oblong, witli a wide and straight hinge-line ; 

 area double; valves radiately striated, articulated; hinge-margir 

 of ventral valve with a series of tubular spines; fissure covered; 

 interior punctatc-striate ; vascular impressions {v) very small. 

 (Davidson.) 



Eossil, 47 species. Silurian — Carboniferous. Europe, North 

 America, Falkland Islands. 



Dorsal valve. 



Fig. 192. 



Ventral valve.* 



Family YI. — Craniad.s. 



Shell orbicular, calcareous, hinge-less ; attached by the umbo, 

 or whole breadth of the ventral valve, rarely free ; dorsal valve 

 limpet-like ; interior of each valve \nih. a broad granulated 

 border ; disk v/ith four large muscular imj)ressions, and digitated 

 vascular impressions ; structure punctate. 



Animal with free spiral arms, directed towards the concavity 

 of the dorsal valve, and supported by a nose-like prominence in 

 the middle of the lower valve ; mantle extending to the edges 

 of the valves, and closely adhering; its margins plaiD. 

 (Fig. 195.) 



Crania, Eetzius. 



Etymology, hraneia, capitate. 



Type, Anomia craniolaris, L. 



Examples, C. Ignaborgensis, PI. XV., Fig. 30. C. anomala, 

 Figs. 193—195. 



Synonyms, Criopus, Poli. Orbicula (anomala), Cuvier, 

 ^=0. Norvegica, Lam. 



* Interiors of two sp. ot Chonetes, from Xehou and the Eifel, after DaWilsont 0^- 

 ej44uctor ; c, co.xcUnals. 



