168 MOLLUSCA. 
aorta arises from each side, to convey the blood to the body. 
The ovarium is placed underneath the liver ; and, as it ex- 
hibits some differences of organization, M. Cuvier infers 
that it likewise contains the male organs. The species be- 
longing to this genus are numerous, and appear to admit of 
distribution into sections; the first having the branchial 
circle complete, the second interrupted. 
Genus Curron.—Shell constituting a series of imbri- 
cated dorsal plates. The body is elliptical. The cloak 
is firm and cartilaginous, and variously marked on the mar- 
gin. The dorsal plates are arched, and occupy the middle 
‘ and sides of the back, where they are implanted in the 
cloak, in an imbricated manner, the posterior margin of the 
first valve covering the anterior margin of the second. The 
foot is narrow. The mouth is surrounded with a semicir- 
cular curled membrane, and is destitute of tentacula. The 
anus consists of a short tube, placed at the posterior ex- 
tremity of the cloak. The external orifice of generation 
has not been detected. 
The mouth is capable of forming a short proboscis. The 
tongue is short, and armed with strong, reflected spines. 
The gullet is short, and the stomach, which is lengthened 
and folded, is membranaceous. The intestine is several 
times longer than the body, and much folded. The liver 
is divided into numerous lobes, and intimately united with 
the stomach and intestines. The heart is situate at the pos- 
terior part of the body. ‘The auricle is placed posteriorly, 
and receives the aérated blood from two veins. Each vein 
descends along the base of the gills, ‘collecting the aérated 
blood from the particular side of the body to which it be- 
longs ; and, what is most remarkable, when opposite the 
ventricle, it is suddenly enlarged, and sends off a branch 
