SPONDYLID^. 285 



strongly impressed grooves to receive the dental processes of 

 the other valve. Fossil, 16 sp. Lias and Lower Oolite; 

 France and England. 



Spondylus (Pliny), Linn. 



Thorny-oyster. 



Syn. — Dianchora, Sby.,1814. Podopsis, Lam.,1819. Pa(!hytes, 

 Defr., 1825. (All based upon casts or imperfect specimens. — 

 Deshayes.) 



Distr. — 68 sp. West Indies, Canaries, Mediterranean, India, 

 Torres Straits, Pacific, West America; 105 fathoms. Fossil, 

 80 sp. Carb — ; Europe, United States, India. S. regius^ Linn, 

 (cxxxi, Yl, tS). S. Americanus, Lam. (cxxxi, 72). 



Shell irregular, attached by the right valve, radiately ribbed, 

 spiny or foliaceous ; umbones remote, eared ; lower valve with 

 a triangular hinge-area, cartilage in a central groove, nearly or 

 quite covered ; hinge of two curved interlocking teeth in each 

 valve ; adductor impression double. 



Animal with the mantle open and gills separate, as in 

 Pecten; lips foliaceous, palpi short; foot small, cj^lindrical, 

 truncated. 



In aged specimens the circular portion of the muscular scar 

 exhibits dendritic vascular markings. The lower valve is alwaj^s 

 most spin}^ and least colored ; in some species (like S. imperialis) 

 the shell is scarcely, if at all, attached by its beak or spines. 

 The inner shell-layer is very distinct from the outer, and always 

 wanting in fossil specimens from calcareous rocks, then called 

 Dianchorge. Specimens from the Miocene of St. Domingo, 

 which have lost this layer, contain a loose mould of the original 

 interior. Water-cavities are common in the inner layer, the 

 border of the mantle having deposited shell more rapidly than 

 the umbonal portion. 



Pedum, Brug., 1792. 



Distr. — Red Sea, Indian Ocean, Mauritius, Chinese Seas. F. 

 Spondi/loideum, Gmel. (cxxxi, 70). 



Shell thin, smooth, compressed, attached by a byssus passing 

 thi'ough a deep notch in the right valve. Inhabits coral-reefs, 

 where it is found half-embedded. 



Terquemia, Tate, 1867. 



Etym. — Dedicated to M. 0. Terquem, an eminent palaeon- 

 tologist. 



Syn. — Carpenteria, E. Deslongchamps, 1858 {non Gray, 1856). 



Distr. — Fossil, 5 sp. Trias — Lias ; France, Germany, Great 

 Britain. T. Heherti^ Terquem. 



Shell inequivalve, subequilateral, attached by the umbonal 

 portion of the right valve ; the left valve slightly concave, 



