GASTEROPODA PECTINIBRANCHIATA. 383 



In some of them, the margin is still digitated. Their animal 

 resembles that of a Murex, but has only a very small operculum(l). 



In others, we merely observe a dentated margin. Their canal is 

 long and straight(2). 



In some again, that margin is entire? they are the Hippocrenes, 

 Montf.(3) 



ORDER VII. 



TUBULIBRANCHIATA. 



The Tiibiilibranchiata should be detached from the Pectini- 

 branchiataj 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 vari- 

 ous bodies : they consequently are deprived of copulating 

 organs, and fecundate themselves. In the 



Vermetus, Adans., 



We remark a tubular shell whose whorls, at an early age, still forra_ 

 a kind of spire, but then continue on in a tube more or less irregu- 

 larly 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 animal, having no power of 

 locomotion, is deprived of a foot, properly so called? but the part 

 vrhich 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. The head of the animal is obtuse, and has 

 two moderate tentacula, on the external sides of which, at the base. 



(1) Sirombus pes pcleca7i{, 'L.,L,\st., 865,866. 



(2) Sirombus fimis, L., List., 854, 11, 12, 916, y. 



(3) Sirombus amplus, Brander., Foss., Hant., VI, 76, or liostellaria macroptera. 

 Lam.; Sir . Jissurella, Lam., Eiicycl. Method., p. 411, 3, a, h, which is not lliat of 

 Martini, IV, clviii, 1498, 1499, Sec. 



