335 
THE COMMON MARINE SHELLS OF THE BOMBAY 
SHORE. 
By A. ABERCROMBIE, 
leveled QU 
(Continued from page 222.) 
THE BIVALVES. 
These shells have received a great variety of scientific names based 
upon the peculiarities of animal formation which the various authorities 
have considered best adapted for their own mode of classification, but 
all are agreed that it is difficult to divide them into well-defined sub- 
classes. 
The authority which we are following places at least three-fourths 
of the Bombay Bivalves, which he calls 
LAMELLIBRANCHIATA, 
under the head of Veneracea, but we shall endeavour to subdivide them 
according to some other writers on more or less marked differences in 
the shells themselves. 
The bivalves have the power of attracting currents of water into 
their shells, which they filter of all nutrimental or shell-producing 
matter it may contain, and then pass out again. 
Some of them accomplish this simply by slightly opening the valves 
of their shells ; others are provided with siphons or fleshy tubes (either 
one with two divisions or two separate ones) which they can protrude 
in varying lengths from the mouths of their shells. 
The opening and shutting of the shells is performed by certain 
muscles, and the number and arrangement of these muscles, as shown by 
the scars left on the interior, is our first help to the classification we 
adopt. Next, the presence or absence of the aforesaid siphons is also 
denoted by scars on the valves, but it is not always easy to detect these 
Scars, especially if specimens are old and worn ; further we have the 
interlocking teeth of the hinge of the shell, which are very variable and 
are a distinct feature in some families ; and, lastly, the ligament holding 
the two valves together is sometimes external, sometimes internal. 
