50 PALEONTOLOGY OF CALIFORNIA. 



FAMILY CEASSATELLIDJ3. 



Genus ASTARTE, Sowerby, 1816. 



Astarte ventricosa, Meek. 



PL 8, Fig. 5, and 5 a. 



Shell of medium size, suborbicular, gibbous; basal aud lateral 

 margins rounded ; beaks moderately prominent, subcentral, or a 

 little in advance of the middle, obtuse and rather tumid ; lunule 

 apparently rather large. Surface ornamented with regular, dis- 

 tinct, concentric ridges, about equalling the furrows between. 



Length and height about 1 inch; convexity near 0.55 inch. 



It is with some hesitation this species is placed in the genus Astarte, since the 

 specimens do not show the muscular or pallial impressions, nor very satisfactorily 

 the nature of the hinge ; while it is a more gibbous shell than is common in that 

 genus. One of the specimens, however, shows an imperfect impression of the 

 hinge of a right valve, which, so far as can be determined, seems to be like that 

 of Astarte. 



There are several more or less analogous European Jurassic species ; but none 

 of tbem appear to be more closely allied to our shell than A. elegans of Sowerby, 

 which is less convex, and differs in outline. Our shell also differs in having more 

 convex beaks. 



FAMILY LUCINEXffi. 



Genus UNICARDIUM, D'Obigny, 1852. 



Unicardium ? gibbosum, Meek. 



PI. 8, Fig. 8, and 8 a. 



Shell thin, rhombic-suborbicular, very gibbous; length some- 

 what greater than the height ; greatest convexity a little above 

 the middle ; beaks nearly central, rather prominent and gibbous ; 



