ASTARTE. 451 



usually lodged in a lozenge. Lunule almost always 

 distinct. 



Animal of the shape of the shell, and never exceeding 

 it ; its mantle freely open, with plain (always ?) margins, 

 slightly united posteriorly at two points so as to form 

 two siphonal orifices, both with simple edges. Foot lin- 

 guiform, strong but not large. Labial tentacles large, 

 lanceolate ; leaflets of each pair of branchiae equal or 

 nearly so. 



This genus is of very ancient origin, species of it appear- 

 ing very far back in time, and abounding during the 

 middle secondary period. The number of living species is 

 inconsiderable as comjjared with the assemblage of them 

 which existed even within our own limited area during 

 some ancient geological epochs. It is curious to note 

 that whilst at present the predominance of Astartes in 

 a collection made at any particular though unknown 

 locality, would lead the conchologist to infer that they 

 had been gathered in an arctic or boreal region, such an 

 inference would, most probably, be incorrect if drawn from 

 a similar assemblage of fossils, for during the oolitic and 

 cretaceous epochs the abundance of Astartes was associated 

 with the presence of numerous tropical or subtropical 

 forms of mollusks and zoophytes. In the upper tertiaries, 

 however, an increase in the number of species and in- 

 dividuals of this genus is usually coincident with the 

 advent of boreal or glacial conditions. 



The members of this genus have a wide range in depth, 

 but are never, at least in our seas, found littoral. They 

 constitute a favourite food of many fishes of the cod tribe. 

 Many of the species are remarkable for presenting varia- 

 tions in the characters of the inner margin and sculpture 

 which, in neighbouring genera, would be of specific, or 



