64 



margined by an acute tooth on each side, to receive 

 the large tooth of the opposite valve ; cartilage groove 

 broad ; space under the apex generally excavated ; 

 muscular impressions two, large ; palleal impression 

 with a profound angular sinus. 



OBSERVATIONS. 



This natural group has been separated from Cythe- 

 rea by authors, who have given it various names ; 

 Schumacher terms it LentiUaria ; Megerle, Orbicu- 

 lus ; and Blainville informs us that Poli has given it 

 the name of Artemis, which I have adopted. The 

 species are all known by their lentiform shape, and 

 differ from each other but slightly in their general 

 appearance. The cartilage is broad and situated in a 

 long groove very like Lucina, and the fosset under 

 the beak is another character which some species of 

 these two genera possess in common ; but the deep 

 sinus in the palleal impression indicates a difference 

 in the organization of the animal, which will distin- 

 guish this genus from Lucina. 



Two species inhabit the southern coast, the Jl. ace- 

 tabulum, nobis, and Jl. concentrica ; both are also 

 found in a fossil state ; the former abundantly in the 

 Pliocene of Virginia, and Professor Mitchell obtained 

 the latter in North Carolina, from a deposit contain- 

 ing a greater proportion of existing species than any 

 of those in Virginia which I have visited. 



