GUDB : ON THE ARMATURE OF LAND MOLLUSCA. 61 



examination of immature specimens has revealed the fact that a new 

 set of palatal lamellae is formed on completion of each half of a 

 whorl, after which the previous set is absorbed by the animal. 

 I have observed several shells which contained two sets of barriers 

 at a distance of half a whorl ; in some cases the older set had almost 

 vanished, only the foundations of the lamellae being visible from the 

 outside through the shell-wall. I have already in the introductory 

 remarks to this address alluded to the fact that whereas in one 

 species — C. adamsi, Gude — the mature shells are devoid of armature, 

 the immature ones are provided with five oblique, palatal lamellae, 

 the same as obtains in the other members of the genus. Ten species 

 are known, all with one exception — C. anax, Bens., which occurs 

 in southern India — being natives of Ceylon. 



In two species — C. heddomecE, Hani., and C anax, Bens. — there are 

 two or three horizontal, curved, parietal, entering folds, while in the 

 other seven Ceylon species the number of parietal folds varies from 

 one to three. One of these — C. hiimherti, Brot — possesses only one 

 short, palatal lamella on the basal wall near the suture, corresponding 

 to the fourth in the other species. The parietal folds are not formed 

 until the shell approaches completion, while the palatal lamellae 

 in the immature shells are invariably much larger than in mature 

 specimens, being almost triangular, overlapping, and reaching nearly 

 to the parietal wall. 



Genus Plectopylis, Benson. 



This genus is divided into five sections and comprises some ninety 

 species, ranging from North-East India through Burma, Tonkin, 

 South and Central China, with one outlying species in the Loo-Choo 

 Archipelago. They all have the interior of the last whorl obstructed 

 by a transverse plate or plates on the parietal wall, and several 

 transverse, oblique, or longitudinal denticles or plates on the palatal 

 wall. In some forms — for instance, P. woodthorpei, Gude, a member 

 of the section Plectopylis, s.s. — the palatal armature is in two 

 series, the anterior set consisting of three thin, horizontal folds, 

 while the posterior series is much more complicated, showing a thin, 

 long, horizontal fold near the suture, a second one below it, still 

 longer, and with an elevated compressed denticle posteriorly, next a 

 very short, curved fold, below this a strong, vertical lamina, indented 

 at the middle and giving off posteriorly at its lower extremity an 

 obliquely descending ridge, where also occurs a small denticle, and 

 on the upper extremity a similar ridge or support ; another long, 

 thin, horizontal fold is found near the lower suture. The parietal 

 barriers consist of two, nearly parallel, vertical laminae, the anterior 

 one the shorter and giving off at each extremity anteriorly a horizontal 

 fold, the lower one short, the upper one revolving parallel with the 

 suture and joining the ridge at the aperture ; below this occurs a free 

 thin horizontal fold, parallel with the lower suture and joining the 

 ridge on the parietal callus. 



