268 MOLLUSCA. 



FuBtrs, Bnig. 

 Comprises all shells with a salient and straight canal, which are destitute 

 of varices. 



TuRBiNEiiA, Lam., 

 Also consists of shells with a straight canal, but without varices, distin- 

 guishable by the large transverse plicae on their columella, which extend 

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

 the conical Volut2e; they only differ from the latter in the elongation of 

 their aperture into a sort of canal. The genus 



Steombus, Lin. 

 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 canal, 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 M. de Lamarck into two subgenera, Sthombtjs and Pte- 



BOCEBA. 



ORDER VII. 



TUBULIBR ANCH I AT A. 



The Tubulibranchiata should be detached from the Pectinibran- 

 chiata, 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. 



Vermetus, Adans. 

 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 enveloped by Lithophytes: the ani- 

 mal, having no power of locomotion, is deprived of a foot, properly so called; 

 but the part %hich in oi-dinary Gasteropoda forms the tail, is here turned 

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

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

 into its shell, it is this mass which closes the enti-ance; it is sometimes seen 

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



