168 MOLLUSC A. 



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 CHITON. 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 aerated blood from two veins. Each vein 

 descends along the base of the gills, collecting the aerated 

 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 



