268 SUPPLEMENT 
In considering, for the present, a bivalve shell composed 
of a single piece as forming a whole, it may be termed long, 
elongated, cylindrical, transverse, &c.; but the application 
of these epithets entirely depends on the position in which 
the shell is placed for study, which, with M. de Blainville, is 
the same as for the univalves. The shell is considered as 
covering the animal, and the latter walking before the ob- 
server, head in front, though in reality few of them change 
place, and they are sometimes in a determinate position on 
the side, or even with the head under. On this depends the 
name given to their forms and proportions, to enter into a 
detail of which in this slight sketch would be quite beyond 
our purpose, and we should but merely repeat what has been 
already said. 
Under the name of multivalve shells we do not understand 
those in which the two valves are covered with a tube, which 
we mentioned above, but only those which are completely 
discovered. 
They constantly appertain to animals which may be said 
to be intermediate between the malacozoaria and the ento- 
mozoaria, or in other words, between the true mollusca and 
the articulated animals. They are so few in number that it 
has been considered nearly useless to establish peculiar terms 
to indicate each of their parts, or such terms enter for the 
most part into those which have been already indicated. 
These parts may be divided, however, into three sections: 
1. The serial, or articulated, so named because they are 
placed in a series one after the other in a symmetrical manner, 
in the middle and dorsal line of the animal. In a great 
number of cases they touch, and even overlap each other more 
or less. ‘This is easy to be recognized, because their anterior 
edge is attenuated, and the posterior the reverse, except the 
first and last, which are rounded, one in front and the other 
behind ; their exterior surface may be smooth or rugous, &c. 
