DB,. eWTN JEFFREYS OK THE GENUS SEGUENZIA. 605 



iimbilicus, which it largely conceals, with a deep narrow furrow 

 behind it. It advances thin and pointed, curving over to the 

 right to its angular junction with the basal lip. TJmbilicus de- 

 fined by a spiral thread and with two other spirals within it. 

 It is not so much small as concealed by the pillar-lip. H. 0*82. 

 B. 0-63, least 0-53. Penultimate whorl 0-19. Mouth 0-4 ; 

 breadth 0-38. 

 Perhaps Trochus {Cantharidus) iris, Humph., while totally 



unlike in most respects, nevertheless approaches this in form 



more than any other shell does. 



Note as to the position of the Genus Seguenzia among the Gas- 

 tropoda. By J. GwTN Jeffeets, LL.D., F.E.S., F.L.S. 



[Read February 6, 1879.] 



The Eev. E. Boog "Watson in a valuable paper, which was Jately 

 read before the Society, on some of the Mollusca procured by the 

 ' Challenger ' Expedition, included the genus Seguenzia in the 

 Trochus family. 



When I described that genus in the ' Proceedings of the Eoyal 

 Society ' (No. 73, 1876, p. 200), I said that it evidently belonged 

 to the Solarium family ; and I gave my reason for this opinion, 

 to which I adhere. I am sorry not to agree with my friend Mr. 

 "Watson ; but such difference of opinion is useful to science. 



The chief points of distinction between the genera of Trochidse 

 and Solariidse consist in the shell of the latter not being pearly 

 or nacreous inside, and in the operculum being ear-shaped and 

 few-whorled, with a lateral nucleus and excentric spire, as in the 

 Littorinidse. The operculum in the Trochidae is circular and mul- 

 tispiral, with a central nucleus. I have fortunately succeeded in 

 extracting the operculum from a small fresh specimen of Seguen- 

 ziaformosa ; and I find it to be ear-shaped, very thin, paucispiral 

 (having two whorls only), the spire being very small, excentric, 

 and placed on the columellar side. It resembles that of Solarium 

 and Adeorhis, genera of the same family. Mr. "Watson says that 

 my account of the operculum represents " a feature, which, accord- 

 ing to Quoy and Gaimard jis shared by Euchelus, Philippi's sub- 

 genus of Trochus.'''' Now all that Philippi remarks as to the oper- 

 culum of Euchelus is, " der Deckel hat nach Quoy und Gaim. nur 

 wenige "Windungen ;" but no mention is made of the shape of the 

 operculum nor of its spire and nucleus. I have carefully examined 



LINK. JOURK. — ZOOLOGY, VOL. XIV. 45 



