BRACHIOPODA. 



235 



CHONETES, Fischer. 



Ex. C. striatella, PL XV. fig. 29. Etym. Chone, a cup. 



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

 double ; valves radiately striated, articulated ; hinge-margin of ventral valve 

 with a series of tubular spines; fissure covered; interior punctate-striate ; 

 vascular impressions (#) very small. (Davidson) . 



Fossil, 24 sp. Silurian Carboniferous. Europe, N. America, Falk- 

 land Ids. 



Fig. 156. Dorsal valve. 



Ventral valve.* 



FAMILY VI. CRANIAM. 



Shell orbicular, calcarious, hinge-less ; attached by the umbo, or whole 

 "breadth of the ventral valve, rarely free ; dorsal valve limpet-like ; interior of 

 each valve with a broad granulated border ; disk with four large muscular 

 Impressions, 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 plain. (Fig. 159.) 



Fig. 157. Ventral valve. Fig. 158. Dorsal valve. 



Crania anomala, Muller. y Zetland. 



a, anterior adductors; a', posterior adductors ; c, protractor sliding muscles; c', cardi- 

 nal muscle, r , o, retractor sliding muscles. 



* Interiors of two sp. of Chonetes from Nehou and the Eifel, after Davidson; a, 

 adductor : c, cardinals. 



