320 Gasteropoda. MOLLUSCA. Toxifeua. 
Sub-Class I. — C T E N 0 B R A N C H I A T A, Gray— 
Prosobranchiata, M. Edwards. 
The cavity in wliicli the gills, in this large group, are 
hinder angle of the gill cavity, and mouth of the shell. 
placed, forms an open hag in the last whirl of the 
The sub-class Ctenobranchiata comprehends within 
shell, over the back of the neck; and there is a con- 
itself the greater part of the Gasteropodous mollusca, 
stant current of water passing over the gills, entering 
whieh are furnished with large and well-developed 
at the front and making its way out near the inner 
shells. 
Order L— PECTINIBKANCHrATA. 
This order contains a larger number of species than any 
greater extent, the teeth are placed in one or several 
other order of Gasteropods, and is divided into three 
rows on the surface of a linear, elongate, cartilaginous 
sub-orders, the characters of which are taken in a great 
tongue-membrane. In the third sub-order, Rostrifera, 
measure from the structure and form of the teeth. In 
the head is produced into a beak or rostrum, and the 
the first sub-order, Toxifera, the head is small, and the 
teeth are disposed in seven longitudinal rows on an 
fleshy proboscis with which it is furnished is retractile 
elongated linear tongue-membrane, partly received 
within the body. The teeth are elongate, awl-shaped. 
into the visceral cavity. This disposition of the teeth 
and implanted in this proboscis. The eyes are sessile. 
seems to be nearly connected with the habits of the 
that is, are not placed on a footstalk, but are situated 
animals belonging to these sub-orders. The Probosci- 
on the outer side, near or on the end of the feelers 
difera. for instance are carnivorous, or animal feeders ; 
or tentacles. In the second sub-order, Prohosci- 
and the Rostrifera are phytophagous or vegetable 
difera, which has the head small and the eyes sessile. 
feeders ; whilst the Toxifera, which are said to feed on 
as in the previous section, but the retractile proboscis 
both animal and vegetable matters, inflict rather severe 
more lengthened and capable of being extruded to a 
wounds upon those who incautiously handle them. 
Sub-order I.- 
-TOXIFEKA. 
The structure of the teeth brings into this group several 
implanted in the substance of this proboseis, are in two 
genera of shells, some of which have hitherto been 
rows, arranged in pairs, and are sharp pointed, more or 
placed wide apart from each other. 
less swollen at the base, but hollow and barbed at the 
tip. The mantle of the animal is entire, covers the 
Family I.— CONIDAl {The Cones). 
interior of the shell, and is prolonged anteriorly into a 
fleshy siphon or canal, cylindrical in form and passing 
We commence with the Cones, a family rich in 
beyond the mouth of the shell, fig. 50 c. This siphon is 
species, and the pride of collectors. The animal of 
open at its free extremity, and its use is to carry the 
the Cones crawls on a long and very narrow foot. 
water to bathe the gills. As the name imports, the 
which is truncated anteriorly, and bears upon its 
shell is of a conical form, with generally a very short 
posterior extremity a small horny annular operculum, 
spire ; in many cases the upper whirls being so com- 
with an apical nucleus. This operculum is very small 
pressed, and the spire so short and flat that the shell 
compared with the size of the shell, is much shorter 
can stand erect when placed upon a flat or even surface. 
than the aperture, and so narrow that it allows the 
The last whirl, indeed, constitutes of itself the greatest 
animal to retract it deeply into the interior — fig. 50 h. 
portion of its whole surface, and terminates at the 
The head is moderately small, and at the extremity of 
base rather by a depression than by a notch The 
the proboscis, which is a prolongation of the head, is 
aperture is narrow, linear — occupying the whole length 
situated the mouth, which is surrounded by a funnel- 
of the last whirl — and having the lips generally straight 
shaped, rostrum-like veil, slit above.* The teeth. 
and parallel. The outer lip is simple and sharp-edged. 
• In the Cones the foot is small and of weak muscular 
cavity, and this cavity it applies to aid its weakness ; for it 
power, says Dr. Johnston, and we might hence conclude that 
performs, like the oral aperture of the leech, the office of a 
the animal possesses little facility in locomotion, “ yet so rich 
sucker, by which the head is readily affi.ved to foreign bodies, 
is all creation,” he adds, “with proofs of contrivances adapted 
Adanson; Senegal, 89. Thus the animal facilitates its progress, 
to annul a defect, that we might anticipate to find some remedy 
and is enabled to drag along the shell, of a weight and size 
here — and it is so. The mouth of the snail is situated in a 
otherwise quite burdensome to it.” — P. 127 
