266 SUPPLEMENT 
be very large, as in the haliotides, which, in consequence of 
this, have received the names of megastomata and macrosto- 
mata; or it may be middling, small, &c. 
The last whorl of the spire may penetrate more or Jess into 
its interior, and modify it. In that case it is said to be so 
modified, as in the argonauts, helices, &c. Then, according 
to the observation of M. de Férussac, the spiral cone is always 
incomplete, but in the contrary case it is complete. It is to 
this part that Bruguiéres exclusively applies the name of 
left lip. 
But above all it may be more or less deeply emarginated 
or entire. This explains the term entomastomata, which 
indicates that the aperture is entire. 
It may show a simple inclination to be emarginated, and 
then it is termed versant. 'This means, that if the shell were 
on its back, and filled with a fluid, the fluid would run out 
through a part of the circumference a little widened. Many 
coni are in this state. ; 
Finally, we may mention the form which has caused it to 
be named siphonostomatous or canaliferous, i. e. when it is 
terminated anteriorly by a canal or siphon, more or less 
elongated ; this form is in relation with a similar disposition 
of the animal itself. 
In the relation of form, which is very variable, the aperture 
of univalve shells may be round, oval, transverse, having 
more breadth than length, angular, semicircular, narrow, or 
linear. . 
The edges of the aperture are sometimes called lips. It is 
divided by a fictitious line, supposed to proceed from one 
extremity to the other of the shell; all which is found to 
correspond to the right side of the animal is properly termed 
labium, and on the other labrum. 
In fine, this aperture of univalve shells may be always 
open, or more or less completely closed by a piece either 
