GORILLA. 55 



in shape and size to those previously observed in the other 

 species. One specimen having completed nearlj' three whorls 

 was ]n-ovided with these barriers at the beginning of the third 

 (post-embryonic) whorl. The natural inference is therefore that 

 these lamellae are formed almost immediately after the young 

 animal is born. 



That structures of this nature serve as a means of defence 

 against the attacks of carnivorous insects and similar creatures 

 was suggested as long ago as 1829 by Guilding, who, in speaking 

 of the teeth and lamin® of the Pupidse, observed that " they may 

 answer the purpose of an operculum to keep out enemies, while 

 they afford no obstacle to the motions of the soft and yielding 

 body of the animal " (Zool. Joui-n. iv, 1829, p. 168, footnote). 

 Of much interest in this connection is a note by Lt.-Col. Godwin- 

 Austin, who, in a paper on tlie genus P/ectopj/lis, states that 

 " when breaking up a number of shells to expose the barriers and 

 ascertain if their characters were constant, I was greatly interested 

 to find in two instances the presence of small insects that had 

 become fixed between the teeth." He further remarks that those 

 shells posssessing such bars to the predatory visits of insects, such 

 as cei'tain kinds of beetles, ants, or even leeches, all of which 

 swarm in the forests where the shells are found, would have the 

 best chance of surviving (Proc. Zool. Soc. 1874, p. 611). 



A careful examination of a number of immature shells, moreover, 

 has revealed the fact that a new set of prjatal lamellae is formed 

 on the completion of each half of a whorl, after which the 

 previous set is absorbed by the animal. I have observed several 

 specimens which contained two sets of barriers at a distance of 

 half a whoi'l ; in some cases the older set had almost vanished, 

 only the foundations of the lamellae being visible from the outside 

 through the shell-wall. 



The fact that C. adamsi upon reaching maturity dispenses with 

 armature gives some scope for speculation. Without being 

 acquainted with the local conditions it is of course im])ossible to 

 solve the problem, but it may be surmised that the absence of 

 predatory insects may have produced this result and that the 

 formation of barriers in the immature shells is simply tue survival 

 of an ancestral character. 



Key to the Sf)ecies. 



A. Mature shell icitlumt internal folds. 



a. Shell larger, diameter 29 mm adamsi. 



b. Shell smaller, diameter 22 mm v. hinidunensis. 



B. Shell tvith internal folds. 



a. Palatal folds oblique. 



a. Two parietal folds beddomece. 



/3. Three parietal folds anax. 



b. Palatal folds horizontal. 



a. One parietal fold humbcrii. 



!3. Two parietal folds odontuphora. 



