492 PHILOSOPHY OF ZOOLOGY. 



the left side, in front, leading to the branchial cavity. A 

 ring of transverse muscles unites the cloak with the foot. 

 On the back is placed the shell, which does not appear on 

 the outside, as it is covered by a thick cuticle. It is lodged 

 in a sac, and united by a muscle, which adheres to the 

 pillar. The hood is produced, at each side, into a flattened 

 tentaculum, with an eye at the external base. The anus is 

 situate at the branchial indentation on the left side. The 

 penis is situate on the right side of the neck ; it is exter- 

 nal, with a crooked, blunt, lateral process near its extremity. 



The mouth is in the form of a short proboscis. The 

 tongue is armed with spines, and is long and spirally fold- 

 ed. The salivary glands are large. The stomach is mem- 

 branaceous, giving off the intestine near the cardia. The 

 intestine makes two folds. The liver, with the testicle in 

 the male, and the ovarium in the female, occupy the pos- 

 terior part of the body, under the spire of the shell. 



2d Subdivision. 



Heart traversed by the rectum. 



This group includes the order Scutibranchia of CUVIER. 

 In general form, and in the structure and position of the 

 branchiae, the resemblance to the genera of the preceding sub- 

 division is very great. They differ, however, in many par- 

 ticulars. The heart is furnished with two auricles, and is 

 perforated by the intestine. The sexes appear to be incor- 

 porated in the same individual, or rather the male organs 

 are unknown. The body is protected by a shell, the aper- 

 ture of which is wide, and never closed by a lid. 



1st Tribe. 



Shell ear-shaped, flat, with a lateral, and nearly concealed 

 spire. 



Family, Haliotida, including the genera Haliotis, Pa- 

 dola, and Stomatia. These genera exhibit well-marked 

 characters in the shell. The left margin of the shell in 



