256 MOLLUSCA. 



whole length of the aperture, and which closely approximate them to the 

 conical Volutse ; they only differ from the latter in the elongation of their 

 aperture into a sort of canal. The genus 



STROMBUS, Linnceus, 



Includes those shells with a canal that is either straight or inflected towards 

 the right, of which the external margin of the aperture dilates with age, but 

 still preserves a sinus near the cunal, under which passes the head of the 

 animal when it extends itself. 



In most of them the sinus is at some distance from the canal. They are 

 subdivided by Lamarck into two subgenera, STROMBUS and PTEROCERAS. 



ORDER VII. 



* 



TUBULIBRANCHIATA. 



THE Tubulibranchiata should be detached from the Pectinibranchiata, with 

 which they are very closely allied, because the shell, which resembles a more 

 or less irregularly shaped tube, only spiral at the commencement, attaches 

 itself to various bodies. 



VEBMETUS, Adanson. 



A tubular shell, whose whorls, at an early age, still form a kind of spire, but 

 then continue on in a tube more or less irregularly contorted, or 

 bent like the tubes of a Serpula. This shell usually attaches itself 

 by interlacing with others of the same species, or is partly enve- 

 loped by Lithophytes. The animal, having no power of loco- 

 motion, is deprived of a foot, properly so called ; but the part 

 which in ordinary Gasteropoda forms the tail, is here turned 

 under it, and extends to beyond the head, where its extremity becomes 

 inflated and furnished with a thin operculum ; when the animal withdraws 

 into its shell, it is this mass which closes the entrance ; it is sometimes seen 

 with various appendages, and in certain species the operculum is spiny. 



MAGILUS, Monffaucon. 



The Magili have a longitudinally carinated tube, which is at first regularly 

 spiral, and then extends itself in a line more or less straight. Although the 

 animal is unknown, it is highly probable that it should be placed near the 

 Vermeti. The 



SILIQUARIA, Brugucir, 



Resembles Vermetus in the head, the position of the operculum, and in the 

 tubular and irregular shell ; but there is a fissure on the whole length of this 



