304 CLAUSILIIDJE. 



found very useful. While the animal is retracted within its shell 

 the elastic pedicle causes the clausilium to rest against the sub- 

 columellar fold on the inner side and against the shorter palatal 

 plicae or the lunella, when present, on the outer side, the anterior 

 angle of its inner margin slightly projecting inwardly over the 

 subcolumellar fold, an arrangement which effectively prevents the 

 clausilium being forced to one side from without, thus securing 

 the animal against intruding enemies. During extrusion of the 

 animal the clausilium is pushed sideways into the groove between 

 the columellar and subcolumellar folds, only its anterior portion 

 being pressed slightly forward at the dilated part of the groove. 

 The clausilium may, therefore, be regarded to act as a sliding door, 

 and while closed during retraction of the animal, the spaces 

 between the palatal plica? are sufficient to admit air for breathing 

 purposes. This peculiar sliding action of the clausilium I have 

 not seen referred to by any of the authors mentioned, which may, 

 perhaps, be explained by the fact that the species which have 

 served as a basis for investigation are rather small and their 

 examination is consequently somewhat difficult. This difficulty 

 may be overcome by utilizing some of the larger Japanese forms- 

 such as 0. nwrtensi, Herkl., and C. valida, Pfeiffer. By the aid 

 of a watchmaker's eye-glass and a needle mounted in a pen- 

 holder, the action of the clausilium can be observed with ease and 

 accuracy. The various folds do not in every species rise at the 

 same point. In some the lower palatal fold rises some distance 

 below the columellar and the subcolumellar folds, in others again 

 the latter rises half way between the other two. The point where 

 the pedicle of the clausilium is attached to the shell-wall, however, 

 is invariably above the termination of any of the folds, at least in 

 all the species both Indian and extra-Indian which I have 

 examined. In all the Indian forms the clausilium has the margins 

 entire, but in some Palsearctic species the margin has a short sinus 

 on the outer side and in others again, the anterior margin is in 

 addition bidenticulate. Five species belonging to the Palaearctic 

 subgenus Alopia, i. e. haueri, cyclostoma, glauca, livida, and lactea, 

 are without clausilium. I must own that at first I entertained 

 considerable doubt as to this, but having by the kind permission of 

 the authorities at the British Museum opened specimens of the 

 species in question, I have satisfied myself that this is actually 

 the case. 



The distribution of the genus Clausilia within the limits of the 

 Indian Empire is somewhat peculiar. Eleven species are known 

 from India but these are all confined to the north, especially the 

 Himalayan region, while none occurs in the whole of southern 

 India, but a single species is known from Ceylon. Burma has 

 no less than fourteen species, while two are found in the Nicobars 

 and the Mergui Archipelago has one, 



A large number of sections or subgenera have been established : 

 one of these Oospira, with five species is confined to Burma, 



