606 DR. GTWN JEFFREYS ON THE GENUS SEGTJENZIA. 



all the species, five in number, oiEuchelus (Aradasia, Gray) in the 

 British Museum, which show the operculum ; and in every species 

 the operculum is more or less circular, and the nucleus is central. 

 In A. cancellata of Krauss and^. haccata of Menke the operculum 

 is at first closely multispiral, as in other Trochidae, although the 

 last whorls more rapidly enlarge. Chenu describes the operculum 

 of Euchelus as " subarrondi." 



Seguenzia formosa has a nacreous exterior ; but ^S^. carinata and 

 S. elegans have the same composition and appearance as the shells 

 of Solarium Jiyhridum and Adeorhis subcarinatus. AH pearly shells 

 do not necessarily belong to the Trochus family, e. g. Turbo, Ha- 

 Uofis, and I^autilus, to say nothing of Anomia, Avicula, and other 

 bivalve shells. 



The labial slit occurs not only in Pleurotomaria, but also in 

 Emarginula, Scissurella, Siliquaria, and the Pleurotomidse, as well 

 as in Seguenzia. 



It is to be hoped that any further doubt as to the systematic 

 })osition of this remarkable genus will ultimately be cleared up 

 by the discovery and examination of the soft parts of the animal. 

 Deep-sea researches have auspiciously commenced : they must be 

 continued and extended. 



N.B. Two species of Seguenzia (viz. formosa and carinata) 

 were fully described by me in the *Annals and Magazine of Na- 

 tural History ' for April 1877, pp. 319 and 320 ; and it surely 

 was superfluous for Mr. Watson to redescribe them at equal 

 length. If every specimen of every species were described in the 

 same way, the literature of natural history would become unne- 

 cessarily voluminous. 



