1919. | N. ANNANDALE & B. PrasHap: Mollusca. 45 
The position of this species is a little doubtful. The shell is 
in some respects intermediate between that of L. peregra (ovata) 
and that of L. lagotis. It resembles somewhat that of L. intermedia 
as figured by Kobelt in the new edition ot Rossmassler’s ‘* Icono- 
graphie” (pl. 488, No. 2602), but the whorls increase more gradu- 
ally in size and the mouth is broader. 
Limnaea bactriana, Hutton. 
(Plo vores: 1.2 capl. wit, te.)6.) 
1850. Lee bactriana, Hutton, Fourn. As. Soc. Bengal XVIII (2), 
p- 656. 
The shell is moderately small, thin, fragile, of a pale, dull 
brownish colour, polished when clean but coated with calcareous 
algae in most of the specimens examined. The surface is often 
irregularly decussated and always bears, at any rate on the body- 
whorl, prominent but narrow longitudinal ridges and correspond- 
ing striae set close together. No transverse striae can be detected 
with a lens. The sculpture is often concealed by the calcareous 
algal coat. The apex is acuminate but not very acute, the spire 
prominent, but occupying less than 4 of the total length in dorsal 
view. The suture is impressed and moderately oblique. There are 
4 or 44 whorls, which are neither swollen nor shouldered ; those of 
the spire increase gradually in size and the penultimate whorl 
is relatively large. The body-whorl is large and of ovoid form; 
its inner outline is markedly sinuate and somewhat emarginate 
towards the anterior extremity, but the antero-internal angle is 
broadly rounded, the outer outline is evenly and not very strong- 
ly curved. The mouth is large but not expanded, extending 
backwards for more than # the length of the body-whorl and being 
less than twice as long as broad; it is of symmetrical ovoid form, 
pointed posteriorly and with its main axis parallel to that of the 
shell. The outer lip is sharp and neither introverted nor expanded ; 
it has a regular and considerable outward curvature and extends 
forwards considerably beyond the limits of the body-whorl. The 
peristome is continuous, the callus broad but thin, extending 
over the narrow but profoundly perforate umbilicus ; the columella 
is distinctly folded. 
As in many species of Limnaea the shellis dimorphic. We shall 
call the two forms (a) and (b) and describe the commoner (@) first. 
(a) In this form the shell has a comparatively long spire, 
occupying nearly } of its length in dorsal view. The 
first 34 whorls increase in size gradually, but the basal 
whorl of the spire is enlarged, the spiralis by no means 
uniform and the body-whorl comparatively narrow. 
(b) The shell differs from that of (@) mainly on account of 
the fact that there is a distinct change in the direc- 
tion of the spiral between the ultimate and pen- 
ultimate whorls. ‘The base of the spire is therefore 
concealed in the body-whorl so that its visible part 
