460 BUCARDIIDiE. 



Species of Adacna. 



colorata, Eichw. plicata, Eichw. 



edentuia, Pallas. vitrea, Eichiv. 



lseviuscula, Eichiv. 



Sub-gen. monodacna, Eichwald. 



Shell transversely ovate, posteriorly gaping, radiately ribbed, 

 smooth. Hinge with a single tooth. 



Caspia, Eichw. pseudocardia, Desh. 



Sub-gen. didacna, Eichwald. 



Shell transverse, ribbed ; beaks produced and posteriorly 

 cariuated. Hinge with two primary teeth. 



Australiensis, Reeve. donaciformis, Schrtet. 



crassa, Eichw. trigonoides, Pallas. 



Fam. BUCAKDIIDiE. 



Labial palps long and narrow. Mantle closed, double- 

 edged, with a pedal opening in front; siphonal orifices close 

 together, sessile, with fringed margins; gills very large, 

 nearly equal. Foot compressed, triangular, acuminate. 



Shell cordiform, ventricose; beaks sub-spiral, wide apart. 

 Hinge with two primary and two lateral teeth in each valve, 

 the anterior lateral teeth sometimes obsolete. Muscular 

 impressions small ; pallial line simple. 



Animal marine ; burrowing in sand. 



