278 DIMYARIA.—VENERIDZ. 
GENUS VENUS. 
This extensive genus, including some of the 
most highly prized ornaments of cabinets, is dis- 
tinguished by a shell usually somewhat solid, 
rounded in outline, or broader than long, equal- 
valved, but somewhat unequal-sided. The surface 
is generally adorned with many concentric ridges, 
often rising into strong ribs, and sometimes divided 
by radiating furrows. The margins are crenate, or 
scalloped; the beaks prominent. The hinge is 
formed of three diverging cardinal teeth in each 
valve. The muscular impressions are round, and 
well marked; the pallial sinus wide and pointed. 
The animal is thick and globose, or oval; the 
edges of the mantle, which 1s open, are fringed. 
The siphons have fringed orifices, generally se- 
parate. The foot 1s not grooved. 
About half-a-dozen members of this beautiful 
genus inhabit the British seas, which are considered 
as nearly the northern limit of its geographical 
range. Of these the finest is Venus casina, of 
which the valves are about an inch and a half in 
diameter. They are marked with strong concentric 
ribs, white, or occasionally painted with two or 
three crimson radiating bands. 
Though this is a rare British shell, it has been 
taken at various localities all round the coast. 
I have obtained specimens from deep water off the 
Isle of Portland. 
FamMiLty MAcTRADA. 
In some respects these shells present close re- 
semblances to those of the last family; but their 
