106 Records of the Indian Museum. [Vo,. XVIII, 
by this race is in itself evidence of a different origin from that of 
the others associated with it—evidence which is greatly strength- 
ened by an examination of the young shell. 
In this discussion we have left L. hordeum out of account. It 
is so different from the other species of the fauna that there can be 
no doubt of its different origin ; there can be little doubt of its re- 
lationship to L. truncatula. It has, however, a larger mouth to the 
shell than that species and more tumid whorls, especially of the 
spire. It has, therefore, followed a line of evolution in some res- 
pects parallel to, in others divergent from, that which has resulted 
in such forms as L. cor. 
Key to shells of Limnaea from S. Persia and Lower Mesopotamia. 
A. Height of mouth less than 3 that of shell.1 
1. Whorls of spire tumid; suture oblique _ .., ... L. hordeum. 
2. Whorls of spire not tumid; suture much less oblique... L. truncatula. 
B. Length of mouth more than % that of shell. 
1. Upper surface of body-whorl not flattened; suture 
above it not canalized. (Height less than 20 mm.) 
a. Mouth of shell projecting strongly in ventral view ; 
arc of lip practically a semicircle... ... WL. persica: 
b. Mouth less expanded, projecting less; arc of lip less 
than a semicircle. 
i. Whorls of spire somewhat tumid 2; suture 
impressed ; main axis of mouth forming an 
acute angle with that of shell. ... ... L. bactriana. 
ii. Whorls of spire not at all tumid; suture little 
or not at all impressed; main axis of mouth 
parallel to that of shell. 
a Arc of lip quite regular; apex sharply 
pointed 2a Sas ... L. tranica: 
8 Arc of lip irregular; apex bluntly pointed. 
+ Arc of lip never more than slightly 
flattened... Ae ... L. gedrosiana. 
* Arc of lip so flattened as to form a 
slanting straight line ... ... L. gedrosiana var. 
vectilabrum. 
2. Upper surface of body-whorl distinctly flattened and 
deeply depressed round suture. 
a. Shell over 15 mm. high, not very fragile, with the 
spire usually about + as long as the body-whorl [fera. 
and the latter much narrower than high .. L. peregra canalt- 
b. Shell not higher than 15 mm., fragile, with the spire 
always less than 1 the height of the body-whorl, 
which is as broad or nearly as broad as high. 
i Spire very small; upper surface of body-whorl 
transverse, almost at right angles to the main 
axis; deeply depressed round suture Br Fay A 
ii Spire small; upper margin of body-whorl cutting 
main axis obliquely, less depressed round suture. L. tenera euph- 
vatica. 
The key applies only to adult shells; for young shells our 
figures in the plates issued with this paper and our former one 
1 Cf. p. 41, Rec. Ind. Mus. XVIII. The specimens now before us show 
that the mouth may be, and probably always is in the adult, more than 3 as long 
as the shell. 
2 On p. 45, line 19 of this volume, the word ‘‘ greatly” has slipped out be- 
tween ‘‘not’’ and “ swollen.’’ 
