GASTEROPODA TUBULiBRANCIIIATA. 



367 



W. lie J,a.marck subdivides these species into two subgenera, fiis !^irornoti.K Tiave the nuter lip dilated into a win^ 



of more or less expanse, but not divided 

 into dif^itations. The foot is proportion- 

 ably small, and the tentacula support the 

 eyes upon a lateral peduncle larger even 

 than the tentaculum itself. The operculum 

 is hui iiy, lon,L,^, and narrow, resting upon a 

 thin tail. Plcrocera-s-, Lam., have the mar- 

 g"in of the full-grown shell divided into long, 

 slender digitatJons, varying in nunjber ac- 

 cording to the species. Tlie animal is the 

 same as in Strombus. 



Other Strombusidsc have the sinus con- 

 tiguous to the siphon. These are tlie lios- 

 iellaria, Lam. They have generally a second 

 canal mounting up the spire, and formed 

 by tlie external lip, and by a continuation 

 of the columella. In some of tbein the lip 

 is digitated. Their animal resembles that 

 of the iluricidcX ; but the operculum is very 

 small. Others have merely denticulations 

 on the lip : their canal is long and straight. 

 Others have the margin entire and plane; 

 and these az'e the Ilippocrenes, Montf. 



THE SEVENTH ORDER OF THE GASTEROPODES. 



THE TUBULIBRANCHIATA.* 



They ought to be detached from the Pectinibranchiata, with which thej' have nevertheless 

 manv affinities, because their shell, in the shape of a more or less irregular tube, and only 

 spiral at its apex, is permanently fixed to other bodies. Thus they have not organs of 

 copulation, and must fecundate themselves. 



Vermetus, Atlanson, — 

 lias a tabular shell, whose whorls, at an early age, still form a kind of spire ; but they are continued on 

 in a more or less irregularly twisted or bent tube, like the tubes of a Serpula. The shell usually attaches 

 itself by interlacing with others of the same species, or by becoming partially enveloped by lithophytes. 

 The animal, having no power of locomotion, is deprived of a foot, properly so called ; but the part 

 \\hich in ordinary Gasteropodes forms the tad, is here turned under, and extends forwards, even beyond 

 the head, where its extremity becomes inflated, and furnished with a thin, [horny, multispiral] oper- 

 culum. Wiicn the animal withdraws into its shell, it is this inflated mass which closes the entrance. 

 It has sometimes different appendages ; and the operculum is spiny in certain species. f The head is 

 obtuse, furnished with two tentacula of moderate size, having the eyes on the outside at their base. 

 The mouth is a vertical orifice : under it we see, on each side, a filament which has all the appearance 

 of a tcntaculum, but which really l)elong3 to the foot. The branchia; form a single [pectinated] line 

 along the left side of the In-anchial ceiling. Its right side is occupied by the rectum, and by the 

 spennalic canal, whieli is also tlie oviduct. There is no male organ. 



The species are pretty numerous, but ili defined. Linnaeus left tlieni among the Serpulte ; and the Vermilia, 

 which Lamarck still allows to stand near Scrpuls, do not differ from the \'eruietus. [This remark is erroneous ; 

 \ei-niilia is a true Annebde, and should be left where Lamarck has placed it.] 



Magilus, Montf — 

 lias its tube keeled its whole length. At first it is pretty regularly spiral, and then is extended in a 

 more or less straight line. Although we do not know the animal, it is probable that its place will be 

 found to be near Vermetus. [The shell is found inclosed in madrepores, bnt not attached to them in 

 any dcree. It would appear that when quite young the animal takes up its station in a hollow part of 



of this order are arraoged amongal the PcctinihTaii- i [This 



' [The 



, hy Kaiif 



ibservation is erroneous, nnd has prohiibly ariae 

 e opercula of SeTJulE for those of a Vcrraetus. 



