GASTEROPODA TUBULIBRANCHIATA. 367 
M. de Lamarck subdivides these species into two subgenera. His Strombus have the 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 Strombusidae 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. 
Fig. 185-Pteroceras Scorpio. ^^^e the margin entire and plane ; 
and these are the Hippocrenes, Montf. 
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 
copulation, and must fecundate themselves. 
Vermetus, Adanson, — 
Has a tubular shell, vffiose 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 branchiae 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 Serpulae, 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. — 
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 w^e 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 degree. It would appear that when quite young the animal takes up its station in a hollow part of 
* [The genera of this order are arranged amongst the Pectinibran- 1 t [This oh^ervation is erroneous, and has probably arisen from mis- 
chiata by Rang 1 taking some operciila of Serpula: for those of a Vermetus.] 
