REPORT ON THE GASTEROPODA. 105 



5. Seguenzia, Jeffreys, 1876. 



Seguenzia, J. G. Jeffreys, Report on the Biology of the " Valorous " Cruise, Proc. Roy. Soc, 



No. 173, 1876, p. 200. 



In all the species of this genus I have seen, besides the infra-sutural sinus resembling that of the 

 Pleurotomacea, there are two others — one, which is rather sharp and slight, at the carina, and another, 

 opener, on the base : between all of these the lines of growth curve out strongly towards the mouth. 

 This might probably be accepted as a generic character. It is a feature very difficult to trace ; but it 

 certainly exists. In a perfect shell the mouth-edge would of course exhibit it ; but all the specimens 

 I have seen are more or less chipped. 



The nacre of the shell is a feature that connects the gonus with the Trochidee. The nacreous 

 layer is evidently not thick ; and when the shell is young and perfectly fresh, it is altogether so 

 translucent that the nacre hardly appears as more than a pearly lustre ; and in all cases it has more 

 of the beauty of the actual pearl than that of the mother-of-pearl shell, but the nacreous layer is 

 unmistakably present. The exterior calcareous layer is thin and very highly translucent, but still 

 not glassy. The operculum of Seguenzia monocingulata, Seg., of which only one specimen has been 

 examined, is by no means characteristically Trochoid, but does not offer a very stable basis for con- 

 necting the genus with the Solariidcc. In that family, very distinctively, the operculum can hardly 

 be considered a well-marked feature ; and far too little is yet known about the genus Seguenzia to 

 make its classification anywhere very satisfactory. This, however, I ought to add, is not the opinion 

 of Professor Verrill, who has had quite recently the advantage of examining a second specimen of 

 Seguenzia monocingulata, Seg., and who has already (see Second Catalogue of N. England Deep Sea 

 Mollusca, p. 186) constituted a new family, " Seguenzidas," having, he says, no affinity either with 

 Solarium (a Ptenoglossa), near which Jeffries placed the group, nor with the Trockidae (Rhipido- 

 glossa), but belonging to the Tasnioglossas. He adds the following details, the confirmation of which 

 will be interesting : — " Operculum thin, rounded-ovate or ear-shaped, with a sub-central nucleus 

 and fine concentric lines. Jaws ovate, with tesselated surface and denticulated edge. Odontophore (in 

 Seguenzia) minute Tccnioglossatc ; the central tooth small, with one denticle ; the inner laterals 

 smaller, with curved unarmed tip ; the two outer laterals slender, sharp, strongly curved." 



Species. 



1. Seguenzia monocingulata, Seg. 3. Seguenzia carinata, Jeffr. 



2. Seguenzia ionica, "Wats. 4. Seguenzia trispinosa, "Wats. 



1. Seguenzia monocingulata, Seguenza. 



Seguenzia monocingulata, Seguenza, Studii stratig. sul. form, plioceniea dell' Italia merid, BolL del Comi- 

 tate Geologico, vol. vii. p. 188, May 1876. 

 „ formosa, Jeffreys, "Valorous" Expedition, Proc. Roy. Soc., No. 173, June 15, 1876, p. 200. 



monocingulata, Seguenza, Cenni intorno le formaz. terz. Reggio Calabria, 1877, p. 27. 

 „ formosa, Jeffreys, "Valorous" Moll., Ann. and Mag. Nat. Hist., April 1877, 1 p. 319. 



1 In the heading of the paper this year is printed by mistake 1876, it was really 1877. 



(ZOOL. CHAIX. EXP. — PART XLII. — 1885.) Tt 14 



