RISSOIDA. 259 
epidermis, exteriorly thickened lip, horny operculum, and want 
of long pointed apophysis. 
TravapiA, Blanford, 1867. 
Distr.—S. ornata, Blf. Brackish water, India. 
The shell has the general form of a Rissoa, but the apex is 
often obtuse, the whorls are spirally ribbed, covered with an 
epidermis ; aperture ovate, with continuous margins, anteriorly 
slightly effuse ; outer lip with an external varix. Operculum and 
‘animal unknown. 
Hyana, H. and A. Adams. 
Distr.—Kuropean. H. vitrea, Forbes and Hanley (1xxi, 22). 
Shell thin, hyaline, elevated conic; aperture oval, slightly 
emarginated anteriorly ; outer lip thin, simple. Operculum 
thin, corneous, simple, subspiral. The tentacles of the animal 
have bristle-like sammits. 
Tatea, Woods. 
Distr.—Tasmania. T. Huonensis, Woods (ixxii, 30). 
Shell elongate-pyramidal. Opereulum calcareous, with a ver- 
tical, submarginal claw. Animal with truncate foot, and long 
tentacles. 
The operculum has the form of that of Rissoella, but differs 
in being calcareous. 
Famity RISSOID A. 
Shell small, spiral, turreted or depressed, often more or less 
umbilicated ; aperture more or less rounded, never truly chan- 
neled in front; peritreme continuous. 
Tentacles elongated, with the eyes at their outer bases. Verge 
(male organ) exserted, situated on the back at a considerable 
distance behind the right tentacle. Gills both pallial; the right 
or principal one usually rather short and broad, and composed 
of few lamin, which are much broader than high. Foot oblong, 
punctate before, rounded or pointed behind. Operculigerous 
lobe well developed. Operculum horny or partly shelly, spiral 
or concentric. Lingual teeth, 31:3; living in fresh, brackish or 
sea-water, sometimes amphibious. Distribution mundane. 
Stoliczka indicates two principal groups in this family: the 
first including the marine genera, with thick, solid Shells, and, 
as a rule, with the labrum externally thickened; the other the 
brackish and fresh-water or amphibious genera, the shells of 
which are usually thin, smooth, with an olivaceous epidermis, 
the labrum not externally thickened. The animals of all the 
Rissoide are very similarly formed, but those living in fresh or 
brackish waters have generally no appendages on the posterior 
portion of the foot, and the operculigerous lobes are less devel- 
oped than in the marine forms. The eye-peduncles are generally 
