113 



one of which is bifid, — in one valve, interlocking with three — 

 the centre of which is bifid — in the other. 



This genus was instituted for the reception of a solitary type of bivalve, 

 plentifully distributed round the British coast in depths varying from a 

 few to eighty fathoms ; but it has a fine representative, amongst others, in 

 West Columbia in Zucinopsis (Artemis) subquadrata. The foot, mantle, 

 and siphons are all different in detail from those of Venus and Artemis, 

 while the shell is of light substance, and, among other equally important 

 differences, has no lunule. 



Species. 



1. decussata, Phil. 5. macilenta, Reeve. 8. substriata, Mont. 



2. gibbosa, Gmel. 6. saccata, Gould. 9. tenuis, Reel. 



3. inflata, Sow. 7. subquadrata, Hanley. 10. undata, Penn. 



4. Kroyeri, Phil. 



Genus 6. ASTARTE, Sowerby. 



Animal ; of the shape of the shell and never exceeding it, its man- 

 tle freely open, with plain margins, slightly united posteriorly 

 at two points so as to form two siphonal orifices, both with 

 simple edges ; foot linguiform, strong, but not large. (Forbes.) 



Shell ; nearly orbicular, generally concentrically strongly ridged 

 and grooved, sometimes smooth, covered by a thick fulvous-chest- 

 nut epidermis ; hinge of two diverging teeth in each valve. 



The genera Astarte and Cyprina possess characters in common which 

 render them somewhat removed from the preceding genera of Conchacea. 

 The animal has no siphons, but simply siphonal orifices, the shell is in- 

 vested in both genera with a stout sombre epidermis, and, with one excep- 

 tion, they are confined to the boreal and arctic seas of Europe and America. 

 A single species of Astarte reaches southwards to the Mediterranean, but 

 Cyprina is not found living in that sea. 



The shells of Astarte are of a uniform dark fulvous-chestnut colour, 

 some are deeply concentrically ridged and furrowed, and some are smooth. 

 They are all of comparatively small size. 



VOL. II. 



