RISSOID AE. 261 
EUCHILUS, Sandberger. Shell small, elongate-conoidal, smooth, 
rimate ; outer lip expanded. Operculum concentric, calcareous. 
Tertiary; Europe. 9sp. H. Deschiensianum, Sandb. (Lxxiii, 4). 
SuspraAMity SKHNHINA. 
Shell depressed, nearly discoidal. Operculum multispiral, 
corneous. Marine. 
SKENEA, Fleming. 
Etym.—Named after Dr. Skene, of Aberdeen, a contemporary 
of Linneeus. 
Syn.—Delphinoidea, Brown. 
Distr.—Northern seas, Norway, and Britain. S,. cornuella, 
Straits of Korea (Adams). 8S. planorbis, Fabr. (1xxii, 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. 
SuspraMity RISSOININZ. 
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 effuse or truncate; the outer lip being peculiarly 
produced either anteriorly or near the middle. 
Rissorna, d’Orbigny. 
Distr. eu eae 100 sp. Tyieeitawacler R. Catesbyana, 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. &. mirabilis, 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. &. tridentata (1xxi, 26). 
ZEBINELLA, Mirch. Shell costellate, spirally striate. &. elegan- 
tissima, d’Orb. (1xxi, 27). 
