Cavolina.i P'JEROPODA. 53 



Fam. CAVOLINIID^E, d'Orbigny. 

 HyalidcB, d'Orbigny. Cleodoridce. Gray. Cliidce, Jeffreys. Orthoconques, Fol, 



Shell external, calcareous, inoperculated. bilaterally symmetrical, 

 not rolled up in a spiral, but at its apex often dorsally recurved. 

 Animal with its pallial cavity ventral, and its columellar muscle dorsal ; 

 the anus situated on the left. 



The shell has a variable form, which may always be referred to a. 

 hollow cone, more or less modified, flattened dorso-ventrally or cir- 

 cular in section. The apex is quite straight, recurved, or truncated ;, 

 the mouth broad or narrow ; with longitudinal or transverse ribs, &c. 

 The initial portion of the shell is generally distinct from the rest, 

 and represents the embryonic shell. 



The animal may be entirely retracted within the shell. The form 

 of the fins and of the posterior lobe of the foot varies considerably. 

 The mouth, the lips, and the tentacles resemble those of. the Limacinidcs 

 (except Peraclis). 



KEY TO GENERA. 



a. Shell larger at the aperture than just behind, constricted behind 



the aperture . . . . . . . . . . . . CUVIERINA. 



b. Shell narrower at the aperture than just behind . . . . CAVOLINA. 



Genus 1. CAVOLINA, Abildgaard, 1791. 



Carolina, Abildgaard, Skriv. Naturhist. Selsk., i, 1791, 173. Type : Anomia 

 tridentata, Forskal. Rheda, Humphreys, 1797. Hyalcea, Lamarck. 1801. 

 Archonta, Montfort, 1810. Tricla, Oken, 1815. Pleuropus, Eschscholtz, 

 1825. Diacria, Gray, 1842. Orbignyia, A. Adams, 1859. 



The special characters of the animal chiefly consist in the breadth 

 of the posterior lobe of the foot, and in the presence of lateral pro- 

 longations of the mantle, which project from the lateral portions of 

 the aperture (side clefts of the adult) and may cover a considerable 

 portion of the shell. 



Shell generally of a horny-brown colour, especially characterized 

 by its much-contracted aperture, which is, however, very broad trans- 

 versely. The lateral portions of this aperture, which are narrower 

 than the middle part, are almost separated from it by a more or less 

 developed tooth rising from the ventral lip and fitting into a dorsal 

 depression. The dorsal lip, which is longer than the ventral, is always 

 more or less ventrally recurved ; the ventral lip, much recurved 

 dorsally, is constricted a little in front of the aperture, and then reflected 

 ventrally. The ventral surface is always bulging. The special form 

 of Cavolinrt depends on the fact that the sides of the shell diverge 

 abruptly outwards, so that the lips appear much prolonged anteriorly.. 

 The sides of the shell are often prolonged into a more or less projecting 

 point. The embryonic shell is not separated by a distinct constriction, 

 except in C. trispinosa and C. quadridentata. 



