CONCHIFERA. 



285 



Vicuna, the mantle-opening for that organ would liave been completely ob- 

 ;ructed by the adductor, but that the muscular support was hook-shaped 

 ig. 200, a). The posterior adductor-process is similarly under-cut for the 

 assage of the rectum, which in all bivalves emerges between the hinge and 

 osterior adductor, winds round outside that muscle and terminates in the 

 ne of the exhaleut current. There is a groove (sometimes an inch deep) 

 3und the second and third duplicatures in the upper valve, which seems in- 

 mded to facilitate the passage of the alimentary canal, and the flow of water 

 om the gills into the exhalent channel. The smallness of the space for the 

 ranchise may have been compensated by deep plication of those organs, as 

 i Chama and Tridacna. 



Fossil, 16 sp. Chalk. Bohemia, Tyrol, France, Spain, Turkey, Syria 

 Jgeria, Egypt. 



Fig. 202. Interior of lower valve. Fig. 203. Interior of upper valve. 



Radiolitesmammillaris, Math. ^ L. Chalk. S. Mamest, Dordogne. 

 ligamental inflection ; m, pallial line; c, c, cartilage pits ; a, a, adductor impressions 

 and processes; t, teeth and dental sockets. 



RADIOLITES, Lamarck, 1801. 

 Etym. Radius, a ray. Syn. Spheerulites, De la Metherie, 3805. 



