BRACHlOPODA. 



335 



Chonetes, Fischer. 



Ex. C. striatella, PI. 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 (t-) very small. (Davidson). 



Fossil, 24 sp. Silurian — Carboniferous. Eiu'ope, N. America, Falk- 

 land Ids. 



Fig. 156. Dorsal valve. 



Ventral valve. 



FAMILY VI. Craniad^. 



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 mth a broad granulated border ; disk with four large muscular 

 impressions, and digitated vascular impressions ; structiu-e 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. \58. Dorsal valve. 



Crania anomala, Muller. i 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 CAowe/es from Nehou and the Eifel, after Davidson; a, 

 adductor ; c, cardinals. 



