﻿r L A iN R B 1 8. 



Plate I. 



r,enus PLANORBIS. Cwftai-.l 

 Jfcilluscum aquatienm. 



Testa !ntrnhn,i ^n'lihtnilix, t!pir<ilif, Jlscoldra, .ipint 

 deprvs^,l ,ti,fr.i,-ti},iif lnl,n< ad >:rplenos : ,qj>'rti(rd 



que tciiiii. 

 Mollusc, freshwater. Sliell spiral, sometimes sin- 

 istral, spire depressed, whorls three to seven ; 

 aperture semilunar, or ovate or trigonal, margin 

 generally thin. 

 Synonyms. GiirelKs, Adams. Orbis, Srhrocl. 

 Iiiclnsis. rianorhald, Hald. Seijineidlnd. 



The late Mr. G. B. Sowerby, in his Gem-ra of 

 Sltclh, expresses his conviction that the Planorbes 

 are sinistral shells, because when the shell is so 

 placed that the aperture is on the left side, the whole 

 of the whorls of what seems to be the spire are 

 visible, while what is then the lower disc is hollow, 

 and the apical whorls are more or less engulphcd. 

 This, however, is not the case throughout the genus, 

 but chiefly among the typical forms. The Messrs. 

 Adams describe the genus as consisting of dextral 

 shells. My impression is that some are sinistral and 

 others dextral. My attention had not been drawn 

 to the subject before several plates had been drawn, 

 and some of the figures being placed as if dextral 

 will seem to have an upside-down appearance. The 

 genus is widely diffused throughout all parts of the 

 globe. Wherever there are ditches, ponds, wells, 

 and rivers, there the Planorbes appear. 



Species 1. (Pig- <', I'. Mas. Sowerby.") 

 Planorbis cobneus. Fhi. testa iiiniidd, Uild, sinis- 

 traU,comed,lcBvigatd,medio aiifracluum castanea; 

 spird. coneavinsciild, aiifradibns senis, convexiils- 



cidh, rapidr cr'/f^rrntihiif:, pmpe siituram rotundis ; 

 turn dfrlirilni.<^ iii/ri'i rmlrirosd; disco inferiori 

 coHcavd, aiijraclibii.': r"tiiiidis, apicalilms ohtectia, 

 apert.urd laid, altd, subiptndratd. 

 The hor^ Planorbis. Shell tumid, broad, sinis- 

 tral, horny, smooth, chestnut in the middle of 

 the whorls ; spire rather concave ; whorls six, 

 rather convex, rapidly increased, rounded near 

 the suture, then sloped, ventricose below ; lower 



disc concave, whorls rounded, apical hidden : 

 aperture broad, high, subquadrate. 

 LiNNsns. Systema Natura?. 

 Hub. Great Britain. 



The specimen represented by figure b belongs to a 

 recently discovered albino variety. 



Species •_>. (Mns, Brit.) 

 Plan-orius trivolvis. I'hi. t.'sid tinuidd, aUd,p,di;d: 



fused, t'bH>iiir nt.jald. .■.■iiiistnd; ; sjdrd r.roinitd, 

 (liigustd, su^irii khI iinim rb'nitd, iiinjiilatil ; au- 

 fraclibus quateruix .vm^i. ,■/(,", Irllms hifenir iippa- 

 reniilnis ; aperturd siililrnjoiid, altd, intiis raslaani - 

 marginatd. 



Tm; turee-whorled Planorbis. Shell tumid, high, 

 pale brown, obliquely wrinkled, sinistral ; spire 

 hollowed, narrow, raised above the suture, an- 

 gular ; whorls, four appearing above, three be- 

 low ; aperture subtrigonal, high, bordered inside 

 with chestnut. 



Sat. American Conchology, ISt'iO. 



Hab. New York. 



Species 3. (Mus. Sowerby.) 



PlaniiUBIS Perijviaxus. Plit. tcsid albidd, sniiipella- 

 cidd, altiuscidd, siuistrali, spird aiirj-ustd, anfrui:- 

 tibus quaternis, angtistis, supra suturarn eleiHitis : 

 ultimo magno, suhdeclivi ; versus aperturani va- 

 lide expanso ; suturd profunda ; aperturd suhtri- 

 gimd, supra infraque anfraatum ultimum productd, 

 disco inferiori cxrarafo, anfracfibus rotvvdis, api- 

 cali obtecto. 



The Peruvian Planorbis. Shell whitish, semipellu. 

 cid, rather high, sinistral, spire narrow, whorls 

 four, narrow, raised above the suture ; last large, 

 somewhat sloped, much expanded towards the 

 aperture ; suture deep ; aperture subtrigonal, 

 produced above and below the last whorl ; lower 

 disc hollow, whorls rounded, the apical one 

 hidden. 



Broderip. Proc. Zool. Soc. 1842, f. 12i. 



Hab. Pern. 



