258 RISSOELLIDA. 
Distr.—26 sp. Ohio River and southwards to Alabama ; 
Southern Atlantic States. A. teeniata, Conr. (1xxi, 17). 
Shell oval, heavy, with very short spire; aperture entire and 
rounded in front ; columella callously thickened above. 
MUDALIA, Hald. (Nitocris, H. and A. Ad.) Shell thinner, 
inflated. Potomac and Susquehanna, Kanawha, and Upper Ohio 
rivers. The distribution is thus more northern than that of the 
type group. A. dissimilis, Say (Ixxi, 19). 
Famity RISSOELLID ®. 
Shell small, thin, transparent, spire elevated, aperture entire, 
rounded or slightly sinuous anteriorly. Operculum corneous, 
concentric. 
Animal with bilobate rostrum, eyes sessile on the head back 
of the tentacles. 
These curious little animals are found adhering to floating sea- 
weeds, in pools between tide-marks; their eyes are situated so far 
behind the tentacles that the transparency of the shell seems to 
be essential to the vision of the animal. The bilobate mouth 
and absence of retractile proboscis indicate them to be vegetable 
feeders. In some respects closely allied to Litiopa. 
RiIssoELLA, Gray. 
Syn.—Jeffreysia, Alder. 
Distr.—6 sp. Britain. On sea-weed, near low-water. (ALDER. ) 
There are eight other species in the Japanese seas. £. diaphana, 
Forbes and Hanley (1xxi, 20, 21). 
Shell minute, translucent. Operculum semilunar, imbricated, 
with a projection from the straight, inner side. Head elongated, 
deeply cleft, and produced into two tentacular processes ; mouth 
armed with denticulated jaws, and a spinous tongue; tentacles 
linear, eyes far behind, prominent, only visible through the shell ; 
foot bilobed in front. 
FAIRBANKIA, Blanford, 1868. 
Distr.—F. Bombayana, Blf. Estuary ; Bombay Harbor. 
Shell imperforate, turreted, with a brown epidermis ; aperture 
suboval, rounded in front; peristome slightly dilated, external 
margin acute, but exteriorly with variciform thickening. Oper- 
culum corneous, subannular with an interior long, transverse 
rib. 
Animal with long filiform tentacles, and eyes sessile at their 
bases; proboscis elongated; foot wide and sinuated in front, 
rounded behind. 
Combines the epidermis, and to a great extent the animal 
of Hydrobia with -the peristome of Rissoa; the- operculum 
approaches that of Rissoella.. It differs from Barleeia in its 
