49 
2. ON A NEW SPECIES OF LYMN#A FROM THIBET. 
By Lovetu Reeve, F.L.S., F.Z.S. ere. 
Lymna Hooxert. Lymn. testd ova- 
éd, tenuiculd, conspicue umbilieatd, 
anfractibus quatuor ad quinque, con- 
vexis, superne depresso-rotundatis, 
suturis subimpressis, aperturd orbicu- 
lari-ovatd, marginibus lamind latius- 
culd subverticali conjunctis ; sordideé 
olivaceo-fuscd. 
The above-described freshwater mollusk, 
collected by Dr. Hooker on the Thibetian 
or north side of Sikkim Himalaya, at 18,000 = 
feet elevation, belongs to the same type as our well-known Lymnea 
peregra, and affords an interesting addition to the evidence which 
has been in part collected touching the wide geographical distribu- 
tion of corresponding forms of plants and animals over those parts of 
Europe and Asia where there are no extensive mountain-barriers. 
The European Lymnea stagnalis has been collected as far east as 
Affghanistan, and the typical form of Lymnea peregra is very cha- 
racteristic in this species from Thibet. A depression of the whorls 
next the sutures, which gives a more orbicular form to the aperture, 
and a conspicuous umbilicus, which is not in any degree covered by 
the columellar lamina, prove it to be specifically distinct from L. 
peregra; and these characters do not appear in the various modifica- 
tions of that species arising out of its more or less ventricose growth, 
or more or less attenuated convolution. South of the Himalaya 
range, where Dr. Hooker reckons the snow-line to be 5000 feet 
lower than on the north side, and 3000 feet lower than the locality 
inhabited by this species, the Lymnee are of quite a different type, 
more especially in the plains of Bengal, where the shell, owing to its 
being formed in so much warmer a temperature, is of stouter growth, 
and characterized by some design of colourmg. The European types 
of Lymnea, ranging over Russia and Siberia, appear abundantly in 
the stagnant waters of North America; and some are identical in spe- 
cies. L. elodes of Say, inhabiting Pennsylvania, is doubtless the 
same species as the European L. palustris; L. truneatula of the 
same author appears to be identical with L. desidiosa; and the L. 
peregra, represented by L. Hookeri in Thibet, is represented in Penn- 
sylvania by Say’s L. catascopium. The Lymnee of Australia are of 
a remarkable and very distinct type from either of those mentioned 
above. 
I have much pleasure in naming this Thibetian Zymnea after the 
indefatigable traveller, whose researches into the natural and phy- 
sical history of that remote country into which few have penetrated, 
are likely to be attended with such important results. - I have placed 
the specimens in the British Museum. 
The figure in outline is of the natural size. 
No. CCIV.—ProceepinGs oF THE ZooLoGicaL Society. 
