82 LAND AND FRESHWATER 
shell in succession, the hind part of the animal remaining all the 
while firmly attached to the surface of the glass. 
*‘ During this operation the horns are partially contracted, and the 
mouth of the animal is applied closely to the shell, and is seen to be 
alternately expanded and contracted, as if in the act of suction. In 
fact the whole process resembles the action of a cat when licking 
its feet and body, and is performed with just the same appearance 
of systematic determination. The object of this operation is no 
doubt the same in both animals—that of clearing their person from 
extraneous matter and producing that aspect of cleanliness and 
beauty which is one of the laws of organic nature in its normal 
state. Hence that brilliant gloss which distinguishes the shell of 
the mollusk here referred to. It would be desirable to ascertain 
whether any analogous habit is possessed by the allied genera Vi- 
trina and Zonites. The shells of the British species of Zonites (Z. 
nitens, alliacea, cellaria, &c.) closely resemble Nanina vitrinoides in 
form, colour, and glossiness of surface, and their brilliancy must 
apparently be due to some polishing action similar to that here de- 
scribed. On the other hand it is difficult to understand how the 
animals of Zonites and Vitrina, whose foot is much broader and 
shorter than in Nanina, should be able to reach every part of their 
shell and purify its surface. 
“The animal of Nanna vitrinoides is of a deep cinereous, the mantle 
yellowish, its lateral projecting lobes darker; the under surface of 
the foot pale grey, with a yellowish stripe along each side.” 
In November 1849 the above gentleman described the same species 
in the Ann. & Mag. Nat. Hist. The size (diameter ;4, inch) and the 
description of the shell agree well with specimens I have in my col- 
lection, collected by the late Capt. A. B. Melville at Jeypur, only 80 
miles from Ajmeer, and which I shall describe in the next Part under 
the title of Macrochlamys stricklandi, for it is certainly not the 
Gangetic delta form. 
No group of shells can be more difficult to identify than those 
that have been classed under this genus. The shells of the larger 
species are so similar in outward form and texture that they are 
very liable to be mistaken at a cursory glance; however, consider- 
able differences are to be found when the animals are examined, 
particularly in the shape and size of the mucous gland at the extre- 
mity of the foot, and in the mantle, its lobes, and varying tongue- 
like lubricating processes. 
I have collected species of this genus for many years over a very 
large area, extending from the Punjab and Mussoorie in the North- 
west Provinces to Assam on the north-east frontier, and I was early 
struck with the very great difference in the colour and form of the 
animal of those shells to which the majority of Indian conchologists 
then gave the name of M. vitrinoides. The shells certainly have a 
very striking similarity, though on a closer examination differences 
in the form, the increase of whorls, &c. can be detected. It is not 
surprising therefore that the whole group stands in a considerable 
