Monograph on the Cj/proeidecBy hy Mr. Gray. 73 



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

 that when the animal has formed a complete 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 j 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 

 ehell, 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 Sabellcey where the animal can withdraw 

 themselves at pleasure ; but in the MoUusca 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 

 Annulosa^ and the shells of MoUusca^ 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 51. Gmelin 126, many of which are 

 twice and three times over, Dillwyn, R. S. 81. Lamarck. Ann. 

 Mus. ^Q. Hist. 98. 



Geographical Distribution. — They are common to the old and 

 new continent, but generally confined to the warmer climates ; 

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

 , Affiniti/.—r-This i'dmilj apTpears to be allied to the sub-family 

 Cassidece amongst the Buccinoidea;, by means of the Cassis Testi- 

 culum, of which Lamarck observes, " ce casque a un peu Pai-pect de 

 certains Cypraea ;" 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 sliell 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 the family, have certainly great 

 afliuity to the Bullideae, as is pointed out by Linueus, who 



