inhabiting India and China. 351 



7. Planorbis ro tula, nobis, n. s. 



Testa minuta, depresso-planata, apertissime umbilicata, luteo-cornea, 

 (liaphana, impolita, spiraliter obsolete striata ; anfractibus 3^, cy- 

 lindraceis, lente horizontaliter increseentibus, supra et subtus sequa- 

 liter apparentibus ; ultimo ad periphseriam rotundato, uullo mode 

 angulato ; sutura supra infraque profunde impressa ; umbilico 

 minime profundo ; apertura vix obliqua, rotundato-lunata ; margine 

 superiori arcuato. 

 Diam. maj. 2|, minor 2, paulo plus, axis 1 mill. 

 Ilab. ill 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 J, axis 2 J. 

 Diam. spirae 3 mill., anfr. ult. 4, supra. 

 PL umbilicalis, Benson, Journ. As. Soc. Calcutta, 1836, vol. v. 



p. 741-2. 

 Hab. in rivis Bengalise orien talis. 



