Monograph on the Cj/proeidece, by Mr. Gray. 73 



is attempted to be explained by Lamarck and others, who assert 

 that when the animal has formed a completfe shell, as It has not 

 the faculty of enlarging its size, it is obliged to quit its shell and 

 form a new one, in the same manner as the Annulosa cast their 

 skins, and by that means the same animal forms many shells ; but 

 I believe there is not the slightest ground for this notion, for 

 these several reasons; 1. If it happens in this genus, it certainly 

 should do so also in several of the other genera, as the Strombi 

 and Pterocerata, where the mouth is fully formed in the small 

 shell, and there is no appearance of varices in the large speci- 

 mens. 2. The muscular attachment of the shell to the animal, 

 is one of the best conchological characters that distinguish this 

 class of animals, from the shelly and sandy cases of the Annulosa ; 

 as the Dentalia and Sabellce, where the animal can withdraw 

 themselves at pleasure ; but in the Mollusca I do not think it pos- 

 sible to be done, but by such force as would destroy the individual. 

 3. There is no analogy between the crust of the Crustacea and 

 Annulusa.) and the shells of Mollusca^ so that it is false reasoning to 

 judge of the possibility of one from the other. 



History. — Rondeletius mentions 4 species. Gesner 2. 

 Aldrovandus 13. Linneus b\. Gmelin 126, many of which are 

 twice and three times over, Dillzei/n, R. S. 81. Lamarck. Ann. 

 Mus. 96. Hist. 98. 



Geographical Distribution. — They are common to tlie old and 

 new continent, but generally confined to the warmer climates ; 

 there are but six or seven species found in the European seas. 



Affinity. — This family appears to be allied to the sub-family 

 CussidecB amongst the Buccinoideae, by means of the Cassis Testi- 

 culum^ of which Lamarck observes, " ce casque a un pcu I'aspect de 

 certains Cypraia;" but the affinity is not slight, for in the shape 

 and form of the aperture, which has a groove or canal at each end, 

 both of the lips plaited, and the front part of the columella flat- 

 tened it accords with those Cyprajae ; but the outer lip is not in- 

 flected, nor is the back of the shell covered with a china-like coat, 

 but with epidermis, and the canal in front of the aperture is recurved. 

 The Ovulae on the opposite side tlie family, have certainly great 

 aflinity to the Bullidex-, as is pointed out by Liniicus, who 



