RISSOID^. 261 



EUCHiLUS, Sandberger. Shell small, elongate-conoidal, smooth, 

 rimate ; outer lip expanded. Operculum concentric, calcareous. 

 Tertiar}^ ; Europe. 9 sp. E. Beschiensianum, Sandb. (Ixxiii, 4). 



Subfamily SKENEINjE. 



Shell depressed, nearlj^ discoidal. Operculum multispiral, 

 corneous. Marine. 



Skenea, Fleming. 



Etym. — Named after Dr. Skene, of Aberdeen, a contemporary 

 of Linnaeus. 



Syn. — Delphinoidea, Brown. 



Bistr. — Northern seas, Norway, and Britain. S. cornuella^ 

 Straits of Korea (Adams). S. planorbis^ Fabr. (Ixxii, 32, 33). 



Shell minute orbicular, depressed, few-whorled ; peristome 

 continuous, entire, round. Operculum multispiral. Animal like 

 Rissoa, foot rounded behind. Found under stones at low-water, 

 and amongst the- roots of Corallina officinalis. 



Subfamily RISSOININ^. 



Shell ovate or turreted; with a thick, corneous, or calcareous 

 paucispiral operculum provided with an internal process (articu- 

 lated). Size small. Marine. 



The genera are well characterized, not only by the form of the 

 operculum, but especially by the form of their aperture, which 

 is anteriorly eflfuse or truncate ; the outer lip being peculiarly 

 produced either anteriorly or near the middle. 



Rissoina, d'Orbigny. 



Distr. — About 100 sp. World-wide. B. Gatesbyana, d'Orb. 

 (Ixxi, 24, 25). 



Shell turreted, whorls numerous, ribbed or cancellated ; aper- 

 ture semilunar, lip slightly thickened within, somewhat expanded, 

 faintly channeled anteriorly. Operculum corneous, thick, semi- 

 lunar, paucispiral, with an interior process. 



issELiELLA, Nevill. (Isselia, Semper, preoccupied.) The em- 

 bryonal shell is sinistral, and von Martens thinks that it should 

 therefore be removed to the neighborhood of Cerithiopsis. The 

 shells do not otherwise differ essentially from Rissoa, and I 

 agree with Dr. Weinkauff that, while the animal and operculum 

 remain unknown, it is better to allow the species to remain in 

 Rissoina. B. mirahilis, Dunker, is the type, and there are sev- 

 eral other Polynesian species. 



ZEBiNA, H. and A. Adams. Shell white, solid, opaque, polished, 

 smooth or partly striate ; outer lip rather thick, with one or more 

 internal anterior tubercles. R. tridentata (Ixxi, 26). 



ZEBiNELLA, Morch. Shell costellate, spirally striate. R. elegan- 

 tissinKf,^ d'Orb. (Ixxi, 2T). 



