413 



SECTION C. VENERACE^E. 



1039. The Veneraceae closely resemble the Cockles in many 

 points of their structure, but their siphons are always greatly 

 elongated (Fig. 697), and furnished with well-developed muscles 

 for their retraction, which are indicated in the interior of the 



shell by the deep sinuation of 

 ~^H *^ e P oster i r portion of the pal- 



<g|)S^ & _____ ll lial line ( see Fi S- 685 )- The 

 ^^^r^Jjj^teB^ f oot is i arge> com p res sed, and 



no. 8.7.-TELLIXA. ? sua % more or less tri a n g ul a r J 



it is employed principally as an 



agent in burrowing. This group includes a considerable num- 

 ber of genera of great interest to the Conchologist ; many of 

 them being remarkable for the beauty of their shells, or for the 

 curious situations in which they live. The greater number of 

 them inhabit sand or mud; but there are several which bore 

 into rocks ; and a few that burrow in masses of coral. The 

 means by which the latter make their excavations are not under- 

 stood. The resemblance both in the shell and the animal, among 

 these numerous genera, is often so strong, as to produce a diffi- 

 culty in their classification, as well as to render it unnecessary 

 to enter here into details respecting them. It will be sufficient 

 to name the genera, Venus, Cytherea, Mactra, Tellina, Donax, 

 Petricola, and Venerupis, as including the greatest proportion of 

 the group ; these being names with which even the ordinary 

 hell- Collector must soon become familiar, on account of the large 

 proportion that the bivalves of this group bear to others, on 

 almost every coast. 



SECTION D. PHOLADACE^. 



1040. The Mollusks of this group are distinguished from those 

 of the preceding, by the wide gape of their shells at the poste- 



VOL. II. G G 



