CIRRHIPEDES. 597 



crs of growth, and the manner in which the valves are se- 

 parable from each other, and from the base ; and by the 

 morbid appearances of the shell, the restraints imposed on 

 its growth by the situation in which it lives, but especially 

 the manner in which fractures are healed, and abstracted 

 "parts restored by the secretion of new matter. It may be 

 added, however, that in the case of the inversely conical 

 shells, the increase probably takes place at the mouth. 



The aperture of the shell is inclosed by the cloak of the 

 animal,, leaving in the centre a tubular or lineal opening 

 for the protrusion of the feet and entrance of the water. 

 This part of the cloak is protected by testaceous plates, 

 which, by their union, form a lid to the mouth of the shell, 

 for the protection of the contained inhabitant. The valves 

 of the lid are four in number, two on each side of the me- 

 sial line, or orifice. In some genera the lateral valves 

 are united. The operculum of this order may, with pro- 

 priety, be compared to the shelly plates of the body of the 

 preceding tribe, and the shelly body of this tribe consider- 

 ed as corresponding to their peduncle, circumstances indica- 

 ted by the muscular attachments of the animal. The con- 

 tinued action of the valves of the lid, obviously assist in 

 wearing down and enlarging the aperture of the shell. 



There is little known, either with regard to the- organs 

 of digestion or respiration, in the animals of this tribe. In 

 their manner of reproduction, they appear to resemble 

 those of the preceding order. ELLIS found the lower part 

 of the shell containing a cavity equal to two thirds of the 

 whole, full of spawn. The genera of this order divide 

 themselves into three families, from circumstances connect- 

 ed with the shell. 



family 1. The shell in this family consists of six valves, 

 and the lateral valves of the lid are divided. It contains 

 five genera. 



