PLECTOPYLIS. 91 



" Palatal armature composed of six short horizontal folds, the 

 first longest, near the suture, provided at its posterior extremity 

 with an elongated denticle ; the second, third, fourth, and fifth a 

 little obliquely depressed posteriorly where they are united by a 

 slight vertical ridge, which is continued above the second and 

 below the fifth folds ; on the posterior side occur five elongated 

 denticles, the four lower of which correspond to the four folds, 



Fig. 38. Plectopylis austeni. 



while the fifth is situate near the upper extremity of the vertical 

 ridge ; the sixth fold is near the lower suture, and has also an 

 elongated denticle posteriorly." (Glide.) 



Major diam. 17'5-iy, minor 14-75-16-5 mm. ; alt. 5-6 mm. 



Hob. Assam : Diyung Valley, Singpho (Ogle). 



The present species is allied to P. oglei, but can readily be 

 distinguished by its concave spire, being besides much smaller 

 and much more flattened. In its parietal armature it differs in 

 having a short and a long median horizontal fold and a denticle in 

 front of the vertical plate, all of which structures are absent in 

 P. oglei. A comparison of the figures will also reveal differences 

 in the palatal armatures of these two species. 



Plectopylis austeni has further, as regards palatal armature, 

 some affinity with P. muspratti, but the latter is dextral and the 

 parietal armature is quite different, as is also the general shape 

 of the shell. 



An immature specimen, which accompanied the three adult ones 

 from which the description was drawn up, has only 5^ whorls 

 completed, and is interesting from the fact that it possesses two 

 sets of armature, a quarter of a whorl distant from each other ; 

 these differ considerably from the mature barriers, the parietal 

 armature consisting of only the vertical plate and a very short, 

 slight, horizontal fold in front of it, while the palatal armature is 

 similar to that of mature shells, except that the folds, ridge, and 

 denticles are very small and slight. 



