MOLLTISCA OF INDIA. 155 



The generative organs (fig. 1 c) present very remarkable variation 

 from tj'pical Macrochlamijs, particularly in the form of the penis. 

 The kale-sac is very long, quite a iiagellum, and close to where the 

 retractor muscle is given off there is a long free csecum loosely 

 coiled ; this undoubtedly represents the closely-wound ca3cum iu 

 the type species, to the side of which the retractor muscle is 

 usually attached. In this species the caecum is quite free, the 

 retractor muscle rising at the base of the cascum itself. The 

 spermatheca is also very long and abnormal in form, consisting of 

 a capacious thin-walled sac at the extremity of a thick muscular 

 stalk-like tube, equal in length to the sac it terminates in. The 

 amatorial organ is thick and large, with a very strong lengthened 

 retractor muscle. 



Here comparison must be made with the generative organs 

 of M. satJiilaensis and M. zemoensis. In both species the penis 

 presents a similar departure from that of typical M. indica ; in 

 both the penis ccecum is free and loosely coiled, merely kept together 

 by a few muscular fibres, whereas in ILindicathis caecum is closely 

 coiled into a mass impossible to unroll, and this is the dominant 

 type over an extensive area of countrj-. 



This departure in form in the Eastern Himalayan species appears 

 to me of considerable interest, one to which I would call the attention 

 of those interested in the gradual modification of special organs. 

 It shows (and it must have been a very slow process indeed) how 

 evolution has aft'ectod morphological changes in this group of 

 molluscs, everywhere so extremely alike in general appearance 

 of their shells, and yet on the extreme limits of their distribution 

 the internal organs present most remarkable divergence in some 

 point or another. 



It might very reasonably be asked whether the description of 

 the markings and coloration of the visceral sac is worthy of record, 

 and until lately I should myself have placed little stress upon it. 

 However, the collection I have been at work upon contains dozens 

 of examples in many species, and of some there are over a 

 hundred. It soon became apparent, when a number had been sorted, 

 how verj' constant, in many cases, was the pattern of the marking, 

 and I found I could sort them out quicker by a glance at the 

 animal than by looking at the shell. The sculpture of this last can 

 always be referred to as another test of identification should any 

 doubt arise. In immature shells the colour- character and markings 

 of the animal are even safer guides, for they begin to show at a very 

 early stage, when the shells themselves are really, in these glassy 

 forms, most difficult to identify. 



Maokochlamys damsangensis, n. sp. (Plate CV. figs. 2-2/.) 



Locality. Damsang Peak, Haling District, Bhutan Dooars. One 

 fully-grown shell and three younger. A number from Ilissom 

 Peak ; one half-grown, Uarhichu, Sikkim. 



