GASTEROPODA TUBULIBRANCHIATA. 



367 



M. de Lamarck subdivides tliese species into two suogenera. His Stromous liave tlie outer lip dilated into a wing 



of more or less expanse, but not divided 

 into digitations. 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 horny, long, and narrow, resting upon a 

 thin tail. Pteroceras, Lam., have the mar- 

 gin of the full-grown shell divided into long, 

 slender digitations, varying in number ac- 

 cording to the species. The animal is the 

 same as in Strombus. 



Other Strombusidoe have the sinus con- 

 tiguous to the siphon. These are the Ros- 

 tellaria. Lam. They have generally a second 

 canal mounting up the spire, and formed 

 by the external lip, and by a continuation 

 of the columella. In some of them the lip 

 is digitated. Their animal resembles that 

 of the Muricidae ; 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 are the Uippocrenes, Montf. 



Fig. 185.— Pteroceras Scorpio 



THE SEVENTH ORDER OF THE GASTEROPODES. 



THE TUBULIBRANCHIATA.* 



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

 many 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 

 copidation, and must fecundate themselves. 



Vermetus, Adanson, — 

 Has a tubular 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 

 which in ordinary Gasteropodes forms the tail, 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. When 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 tentaculum, but which really belongs to the foot. The brancliia; form a single [pectinated] line 

 along the left side of the branchial ceiling. Its right side is occupied by the rectum, and by the 

 spermatic canal, which is also the oviduct. There is no male organ. 



The species are pretty numerous, but ill defined. Linnaeus left them among the Serpulae ; and the Vermilia, 

 which Lamarck still allows to stand near Serpula;, do not differ from the Vermetus. [This remark is erroneous ; 

 Vermilia is a true Annelide, 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 tlie animal, it is probaljle that its place will be 

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

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



are arranged amougst the Pcf.tiuibr^ 



* [Tlie genera of thi: 

 citifita by Hang 



t [This ob.scrvation is erroneous, anrt has probably arisen from mis- 

 taliing some opcrcula of Scrpulx for those of a Vermetus.] 



