AKTHKOPODA. 73 



Order II. APODA. 



" Carapace reduced to two separate threads serving for attach- 

 ment." Body without cirri. Mouth suctorial. 



Proteolepcts bicincta is the only member of this order. It is like 

 the larva of an insect, about one fifth of an inch long, and parasitic 

 on Alepas cornuta. Its earlier stages are unknown. 



Proteolepas. 



Order III. ABDOMINALIA. 



" Carapace flask- shaped." Thoracic segments without limbs ; 

 the abdomen with three pairs. Two eyes. Mouth extensile. 

 Sexes distinct. 



The members of this order are all burrowers in shells. Cryp- 

 tophialus minutus, the only species of the genus known, is one 

 tenth. of an inch in length, and is lodged in a flask-shaped cara- 

 pace. " The early larval stages are passed under an egg-like 

 condition within the sac of the parent." The pupa, having no 

 natatory limbs, crawls about by the aid of its antennae. Cock- 

 lorine burrows in the shells of Haliotis ; Alcippe is found on our 

 own coasts, in the shells of Fusus and Buccinum. 



Cryptophialidce . Alcippidoe. 



Cryptophialus. Alcippe. 



Cochlorine. 



Order IV. THORACICA. 



" Carapace either a capitulum or a pedicel, or an operculated 

 shell with a basis." Six thoracic segments with six pairs of limbs. 

 Two eyes. 



In this order are two primary forms, the pedunculate and the 

 sessile. In the pedunculate forms the peduncle is formed by a 

 modification of the larval antenna. The sessile forms are pro- 

 tected by a strong inulti valve conical shell closed by a four-valved 

 operculum. " The whole shell has a cellular and organized texture, 

 and its gradual expansion is provided for by the successive growth 

 and calcification of processes of the mantle which penetrate the 

 uniting sutures." The cement fixing the animal is secreted by an 

 organ which Darwin has shown to be a modified portion of the 

 ovarian tube. 



The soft parts and cirri are subjected to a periodical moult, 

 not, however, affecting the shell. 



