Order 7. 



GASTEROPODA TUBULIBRANCHIATA. 



359 



M. de Lamarck subdivides these species into two subgenera. Hia Stromous liave the outer lip dilated into a win^ 



of more or less expanse, but not divided 

 into dii^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 horny, long', and narrow, restinjj upon a 

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

 pin 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 Strombusidce liave the sinus con- 

 tiguous to the siphon. These are the Ros- 

 iellaria, 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 iMuricida; ; 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 Hippocrenes, Montf. 



rig, 185.— Pleroceras Scorpio. 



THE SEVENTH ORDER OF THE GASTEROPODES. 



THE TUBULIBRANCHIATA.* 



They ought to he fletached from the Peetinibranchiata, 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 i)ennanently fixed to other bodies. Thus they have not organs of 

 copulation, and must fecundate themselves. 



Vermetus, Adanson, — 

 Has a tubular shell, whose whorls, at an early age, still form a kind of spire ; l)ut they are continued on 

 ill 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 lithopliytes. 

 The animal, having no power of locomotion, is deprived of a foot, projjerly 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 tlie entrance. 

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

 obtuse, furnished with two tentacula of moderate size, having tlie 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 branchiae form a single [pectinated] line 

 along tlie left side of the braucliial ceiling. Its right side is occupied liy 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 tlie Serpnls ; and the Vermilia, 

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

 Vermilia is a true Annelide, and should be left where Lamarck has placed it.] 



Magilus, Montf. — 

 Has 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, but not attaclied to them in 

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



• [The genera of this order nrc ,irrnn(!»d amongst ItiC rcrtluihnin- 

 chinta by Rang 



t [Tills obscr^'.itlou is erroneous, and has probably arisen from mis 

 takini; some opcrcula of Scrjmla; for tliose of a Vermetus 



