50 EOCENE MOLLUSCA. 



Li the 2d ed. of Lamarck, torn, viii, p. 120, the author says, " toute sa surface est 

 couverte de striae longitudinales." 



In the present species, the pedal region, from the margin to the elevated ridge or most 

 tumid portion of the shell, is quite free from striae of any kind ; and on the centre the striae 

 are small, close, and numerous, becoming larger and wider as they diverge from the middle 

 towards both regions; the hinge-line is short, and there is a small gape or sinuation in the 

 siphonilateral margin immediately under the auricle ; the umbo is small, sharp pointed, 

 but not very prominent, unlike that represented in the French shell, which has also appa- 

 rently a greater height. With these differences, I have ventured to propose for the English 

 fossil a new name. 



SPONDYLUS. Linn., 1767. 



Spondylus. Rondelet, 1555. List., 1686. 

 Spondylites (sp.). Aldrov., 1G48. 

 Argus et Argoderma (sp.). Poll, 1795. 

 Plagiostoma (sp.). Lamk., 1819. 

 Dianchora. J. Sowerby, 1814. 

 Podopsis. Lamk., 1819. 

 Pachytos. Defrance, 1825. 

 Pachyta. Menke, 1830, fide Herrm. 

 Pachytus. Agass., 184/. 



Generic Character. Shell irregular, generally thick and strong, and attached by the 

 right valve ; ribbed or costated radiately ; more or less spiny or foliaceous ; eared ; umbones 

 often remote ; lower or attached valve with a triangular hinge-area ; connexus bipartite, 

 cartilageous portion between two curved interlocking teeth in each valve ; impression by 

 the adductor double. 



Animal with the edges of the mantle disconnected as in Pecten, and furnished with 

 two rows of tentacular filaments ; foot small, cylindrical, truncated. 



The species of this genus in the recent state are about thirty, and these are distributed 

 over the globe, but mostly in tropical or subtropical regions ; many of these are beautifully 

 coloured, and highly ornamented with spines or broad foliaceous projections ; these 

 appendages are sometimes long and pointed, while at others they are merely rudimentary 

 spines. These shells are known by the name of spiny oysters, but they are wholly 

 distinct from the genus Ostrea, and approach nearer to Pecten, which they resemble 

 in some characters. The hinge-area is furnished with prominent denticles, two in 

 each valve ; those in the lower are small, and situated close to the cartilage ; the two 

 teeth of the upper valve are more remote, and lock into depressions outside the smaller 

 teeth of the lower valve. The connexus is more or less internal, opening the shell by 



