286 PALEONTOLOGY. 



Recent Sjiecies. 



LAXICAVA. 



L. cALDERENSis, Coiirad. Ovate-oblong ; of a chalky whiteness ; inequilateral ; anterior and 

 posterior margins acutely rounded ; anterior side with hroad, flattened, waved radiating ribs ; 

 posterior side with narrow, sub-acute, radiating, more promineat ribs ; an oblique wide space 

 on the disk without radii, or they are obsolete ; surface with closely-arranged prominent wrin- 

 kled lines, larger posteriorly. 



