44 



Family 2. COLUMELLATA. 



Shell ; emarginated at the base, with the columella strongly ob- 

 liquely plaited. 



The genera of pectinibranchial gastropods constituting the family Colu- 

 mellata, all included by Linnaeus under the head of Voluta, are mainly 

 characterized by the presence of four or five conspicuous plaits winding 

 obliquely round the columella, with a notch at the base, or rather front edge 

 of the shell, viewing it in its natural position upon the animal, for the 

 passage of the respiratory siphon. A modification of this structure appears 

 also in some genera of Canahfera, as in Turbinella, and Cancellaria ; not 

 only, however, are the plaits in that family more limited in number and 

 more feebly developed, but the genera are allied by other characters of 

 greater importance. The Auricula shells are, in like manner, characterized 

 by a plaited columella, but they again are the production of animals dwelling 

 in fresh and stagnant water, whose physical condition is necessarily adapted 

 to the different medium they inhabit*. 



In reviewing the soft parts of the Columellata it may be observed that 

 they are very much larger and more expansile in some species than in 

 others ; the Marginella, have the mantle expanded entirely over the shell, 

 as in Cypraa ; in Cpnbium the disc is very large and muscular, the shell 

 light and ventricose, whilst the mantle of that genus, as well as of Voluta, 

 is in some instances partially expanded over the shell. The animal of 

 Mitra, on the other hand, is small, the shell often solid and ponderous, 

 with a thick fibrous epidermis, and there is no outward expansion of the 

 mantle, whilst the proboscis is capable of extraordinary elongation. 



The genera of tins family are extremely rich in species, but of those 

 referred to it by Lamarck and Deshayes, I remove Columbella to the family 

 Purpurifera : first, on account of the absence of plaits on the columella, 

 and, secondly, because of its nearer affinity with Purpura and Ricinula ; 

 in place of this a new and interesting genus has to be inserted after Mar- 

 ginetta, founded by M. Deshayes upon a little inhabitant of the Mediter- 

 ranean, under the name of Ringicula. 



Cymbium. Mitra. Eingicula. 



Voluta. Marginella. 



* Mr. Swainson had a notion that every character in Zoology, however unimportant, is repre- 

 sented in complete analogy throughout the different classes of animals, within very prescribed 

 limits ; he conceived, for example, that the Volutes and Mitres represent the Basorial type 

 among Birds, the Ungulata among Quadrupeds, and the Thysanura among Insects. These nights 

 of analogy he proposed to exhibit in circles ; and they revolved in his imagination in such mys- 

 tical order as to reveal the most incomprehensible affinities. 





