CONCHOLOGY. 85 



S. longispineus. The long-spined Spondylus. 



Thickly spined, longitudinally sulcated and ribbed ; alter- 

 nate spines arcuated and tongue-shaped ; valves of a reddish 

 colour ; umbones orange. 



7. Podopsis. Two fossil species. 



Only introduced here to fill up the family and keep up the 

 chain of connexion. It approximates the genus Gryphea. 



Shell rather thick, sub-regular, symmetrical, equilateral, 

 inequivalve, adhering by the extremity of the shorter valve ; 

 the other terminated by a summit pointed, a little recurved 

 and medial ; articulation very angular, by means of two very 

 distant condyles. 



FAMILY XIX. 



OsTRACEA. Six genera. 

 1. Gryphaea. One species. 



This genus resembles the Ostrea, with which it was for- 

 merly classed, but from which it is distinguished by the pe- 

 culiar character of the lower valve. It is very deep and 

 carinated, with a summit terminating in a long spirally re- 

 curved beak, slightly turned to one side ; the edge sharp and 

 angular. 



It is seldom, if ever, attached to other bodies. Shell more 

 finely lamellated than that of the oyster, free or slightly ad- 

 herent, sub-equilateral, very inequivalve ; the lower valve 

 very concave, with a summit more or less recurved like a 

 hook ; the upper valve much smaller, and formed like a lid ; 

 hinge without teeth; ligament inserted in an oblong arched 

 cavity ; one single muscular impression on each valve. 



G. angulata. The angulated Gryphaea. PI. 16, fig. 2. 



Oblong ovate, with three long longitudinal carinated ribs 

 below ; summit of the inferior valve is subvolute. This is a 

 rare shell. 



