400 VENERIDiE. 



tirely united to their extremities, where the orifices are 

 surrounded by fringes of cirrhi. Foot linguiform, apicu- 

 late, not furnished with a byssal groove ; labial tentacles 

 lanceolate. 



This beautiful and extensive group of bivalves includes 

 more than a hundred distinct forms, of which the majority 

 are remarkable either for elegance of shape or brilliancy of 

 colour. But few of these range to the British Seas ; 

 those which do, however, are among our most attractive 

 shells. Since northwards of our region these are not re- 

 placed by new forms, we may regard ourselves on the out- 

 skirts of the generic province, especially as the majority of 

 Veneres, and the larger and more beautiful kinds are either 

 tropical or subtropical. The vertical range of the several 

 species is very variable, extending from low-water mark to 

 great oceanic depths. Some kinds are confined to the 

 water''s edge, others inhabit exclusively the abysses of 

 ocean, whilst not a few have very extensive ranges, as in 

 the instances of Venus striatula and Venus ovata, both of 

 which live indifferently at the margin of the sea, and be- 

 neath a depth of more than one hundred fathoms. Such 

 capacity for enduring great differences of pressure warn us 

 not to lay too great stress on that influence as a regulator 

 of distribution, the more so as examples of these mollusks 

 drawn suddenly up from very great depths appear to expe- 

 rience no inconvenience from the rapid change of conditions, 

 and display their siphons and other organs as readily in a 

 basin of sea-water as they could ever have done in the pro- 

 found recesses of their birth. 



Whilst some conchologists object to the separation of 

 Venus from Gytherea and Tapes, others would divide this 

 group into numerous lesser genera. Thus, Venus casina re- 

 presents the genus Clausina of Brown ; Venus striatula his 



