88 CLASS GASTEROPODA. 
have no copulating organ, but fecundate themselves. Their 
heart does not embrace the rectum, but varies as to situation. 
But two genera of this order are known, in both of which the 
shell never approaches in the least to the turbinated form. 
PATELLA, Lin. 
The entire body covered with a shell, formed of a single 
piece, in the form of a broad-based cone; a cordon of little 
branchial lamella under the margin of the mantle; the anus 
and genital orifices somewhat to the right and above the head, 
which is furnished with a thick and short snout, and two 
pointed tentacula, on the external base of which are the eyes; 
the mouth is fleshy, and containing a spiny tongue, which in- 
clines backwards, and is reflected deeply in the interior of the 
body. ‘The stomach is membranous, and the intestine long, 
thin, and greatly flexed; the heart is forwards, above the neck, 
and a little to the left. 
Some species abound on the coast of France. 
CHITON, Lin. 
A range of testaceous and symmetrical scales along the back 
of the mantle, but not occupying its whole breadth ; edges of 
the mantle coriaceous, and furnished either with a naked skin 
or little scales, which give it the appearance of shagreen, or 
with spines, hairs, or setaceous fasciculi. Under these edges, 
on each side, is a range of lamellar, pyramidal branchie ; and 
before, a membranous veil on the mouth supplies the want 
of tentacula. ‘The anus is under the posterior extremity. 
The heart is situated behind, on the rectum; the stomach is 
membranous, and the intestine very long and greatly con- 
torted. ‘The ovary is situated over the other viscera, and ap- 
pears to open on the sides by two oviducts. 
A few small species are found on the coast of France; very 
large ones abound in the seas of hot climates. 
