inhabiting India and China. 351 
7. Planorbis rotula, nobis, n. s. 
Testa minuta, depresso-planata, apertissime umbilicata, luteo-cornea, 
diaphana, impolita, spiraliter obsolete striata; anfractibus 34, cy- 
lindraceis, lente horizontaliter increscentibus, supra et subtus eequa- 
liter apparentibus ; ultimo ad periphzriam rotundato, nullo modo 
angulato; sutura supra infraque profunde impressa; umbilico 
minime profundo ; apertura vix obliqua, rotundato-lunata ; margine 
superiori arcuato. 
Diam. maj. 22, minor 2, paulo plus, axis 1 mill. 
Hab. in agro Rohillano, prope urbem Moradabad, raro occurrens. 
This is the most agile freshwater mollusk which has ever 
fallen under my observation. I discovered it in 1841, on high 
ground westward of a house belonging to the Nuwab of Rampore 
at Moradabad, which became flooded during heavy rain, and 
which had no communication with tank, marsh, or other body 
of water. The shells must have lain under ground during at 
least nine months in the year, and I failed to find them in the 
same spot at the corresponding season in subsequent years. The 
little animal suspended itself below the surface in the shallow 
water, and projected itself at a rapid rate by a series of quick 
and sudden jerks, the disc of the shell acting below as a kind of 
oar. The sudden starts called to mind the manner of the oceanic 
Pteropodes. The motions of Pl. compressus and other allied 
species exhibit nothing similar. I had ample opportunities of 
ascertaining this point from having kept P. compressus for 
months in a glass vase in which I watched its habits. Pl. rotula 
is thus enabled to escape from the drying-up shallows, and to 
enjoy, for as long a period as possible, its short-lived liberty, 
which a slower mode of progression would much tend to abridge. 
The inaccessibility of the work, in which I originally described 
the two following species, to the generality of readers, induces me 
to take advantage of the present opportunity of redescribing them 
more fully. Comparative remarks on the species, and other ob- 
servations on the genus, will be found on reference to the journal 
quoted. 
8. Planorbis umbilicalis, nobis. 
Testa polita, luteo-cornea, subopaca, leviter radiato-striata, supra con- 
vexa, spira planulata; apice concavo; sutura impressa; anfractibus 4, 
ultimo extus depresso, majusculo, inferne obtuse angulato, infra 
planiusculo, majori, versus umbilicum subapertum, profundum 
declivi ; apertura obliqua, subcordata, margine superiori arcuato, 
prominente, inferiori recedente. 
Diam. major 7 mill., minor 5}, axis 2}. 
Diam. spire 3 mill., anfr. ult. 4, supra. 
Pl. umbilicalis, Benson, Journ. As. Soc. Calcutta, 1836, vol. v. 
p- 741-2. 
Hab. in rivis Bengaliz orientalis. 
