MARINE MOLLUSCS 



211 



The shells of the various species are usually of a graceful oval or 

 oblong form, frequently marked by chevron-shaped lines in pretty 

 colours, and distinctly grooved along the lines of growth. The 

 ligament is external, the hinge has usually three diverging teeth in 

 each valve, and the pallial line is sinuated. 



The principal genus is Venus, in which the shells are ovate in 

 form, thick, and smooth, and the margins of the valves are minutely 

 crenulated. The genus is a very large one, and contains several 

 British species, two of which we represent in the accompanying 

 illustrations. 



Allied to these is the larger but pretty shell Cytherea chione, 

 which inhabits deep water off the southern coasts, to about one 



4 3 



FIG. 143. Veneridre 

 \. Venut fasciala. 2. Venus ftriatula. 3. Tapes virgineana. 4. Tapes aurta 



hundred and fifty fathoms. It is much like the Venus shells in 

 form, but the margins are not crenulated. 



The same family (Veneridce) contains the large genus Tapes, so 

 called because many of its shells are marked in such a manner as to 

 recall the patterns of tapestry. The general form of these shells 

 is oblong, and the margins are quite smooth. They are frequently 

 washed up on the beach, especially during storms, but the animals 

 may be found alive at low water, buried in sand, or hiding in the 

 crevices of rocks or among the roots of the larger sea weeds. The 

 mantle is open at the anterior end, and the siphons are either quite 

 distinct or only partly united. 



Some of the shells are very prettily coloured. One (T. aurea) 



