CHAP> VIII. SIGARETUS, AND ITS PROTOTYPES. 235 



SO far as that its circumference is fitted into a fleshy 

 rim. The aspect of Quoy's Cryptostoma again, and of 

 Blainville's, are much the same ; and neither of these 

 agree with the delineation of the animals of De Blain- 

 ville's Sigaretus, Vetulina, or Coriocella. In the pre- 

 sent difficulties, in short, which surround this question, 

 we shall leave it for the investigation of others : our 

 impression is, that part of the Sigareti of authors be- 

 long to the Naticidce, and part to this group ; and 

 that these can only be determined by the structure of 

 their animals. In the meantime we have no great hesita- 

 tion in considering De Blainville's Coriocella and Velutina, 

 in conjunction with Quoy's iS'/^are^ de Tonga, as sub-ge- 

 nera of that genus which intervenes between Calyptrfjea 

 and Crepidula, and which we provisionally call Cheli- 

 NOTus, from the resemblance which the typical forms bear 

 to the back of the tortoise. The animals of all these have 

 two short, thick, cylindrical tentacula ; the eyes being 

 at their base, and either sessile, as in Coriocella, or at 

 the tip of short peduncles (which are united to the ten- 

 tacula), as in Chelinotus* We believe, also (judging 

 only from his figure), that De Blainville's Sigaretus con- 

 vea:usf belongs also to this group, since the animal 

 merely differs from the Coriocella and Chelinotus in not 

 having the anterior part of its mantle forked, and being 

 very little larger than its shell, which thus becomes 

 external. As for the shells themselves of these genera, 

 they seem to be all of one form, precisely like that of 

 Vitrina, which they obviously represent : hence they 

 are not of primary importance in determining the ques- 

 tion. As for the Sigareti of Lamarck, Sowerby, &c., 

 we suspect that when their animals become known, they 

 will turn out to belong to the NaticidcE, since, so far 

 as the shells are concerned, we have a most perfect 

 series by which they seem to be connected with the 

 Natica mamilla of authors ; while Cryptostoma may 

 possibly be the tectibranchian type of that family, just 



* Si'garet de Tonga, Quoy, Voy. d'Astrolabe, pi. 66. bfs, figs. 4 — 8. 

 + Manuel, pi. xlii. fig. 2. 2 a. 



