238 SHELLS AND SHELL-FISH. PART I. 



we know not^ at present, the limits between the two. 

 We could extend these analogies into the vertebrated 

 animals ; for they are not only manifested among the 

 reptiles by the Chelonides or turtles, but by the arma- 

 dillos, in the order of ruminating quadrupeds, the Cas- 

 sidce, or tortoise beetles, among the coleopterous insects ; 

 and, in short, throughout the whole animal kingdom. 



(219.) Leaving, therefore, the true affinities of the 

 Sigareti of authors undetermined, we may proceed to 

 the genus Crepidula as the last we place in the present 

 family. W e know not by what form, if any, it is con- 

 nected to Chelinotus, but its affinity on one side to Na- 

 vicella, and consequently to the nerits, has been long ad- 

 mitted ; while to Haliotis it is as obviously connected by 

 means of Crep. aculeata, and such other ear-shaped spe- 

 cies as have defined spiral whorls placed on one side of 

 the shell, as in the Haliotida. Hence it follows that Cre- 

 pidula stands at one side of the circle of the Haliotidce, 

 connecting them with the NaticidcE, and Calyptnea at the 

 other, connecting them with the Trochid(S ; it Tollows, 

 therefore, that they cannot be united by affinity, except 

 indeed on our theory, that the three aberrant groups 

 always form a circle of their own. 



(220.) Our fifth and last family is that of the 

 NaticidcB, or nerits, consisting of those genera whose in- 

 habitants are not furnished, like the Twr6ic?«, with a pro- 

 boscis-formed mouth, and eyes placed upon their antennae, 

 but whose mouth is like that of the generality of shell- 

 fish belonging to this tribe, and whose eyes, where they 

 exist, are at the base of their tentacula. The animal of 

 one of the typical NaticidcB has been beautifully drawn 

 by Guilding, and is here copied (^jig. 43.) ; it is a most 

 extraordinary looking creature. The whole family differs 

 from the Trochidce, moreover, in having no lateral fila- 

 ments; and in the form of their lips, eyes, &c.; and from 

 the Haliotida, in all that respects the animals, as well as 

 their shell. For reasons, however, which we have just 

 before this detailed, this is the only family whose analysis 

 we find it impossible to complete : this originates in the 



