5o8 Records of the Indian Museum. [Voi.. VIII, 



fold, close to, and parallel with the lower suture and continued 

 posteriorly and anteriorly into a very slender fold, the posterior 

 portion about 3 mm. in lengthy but the anterior part running as 

 far as the edge of the parietal callus. On the posterior side of the 

 plate occur two denticles, one in a line with the upper, and the 

 other even with the lower extremity. 



The palatal armature consists of: 1°, a short, low, horizontal 

 fold near to and parallel with the upper suture ; 2°, a longer, 

 stouter fold, its anterior portion horizontal, next curving down- 

 wards in a semicircle, and its posterior portion again horizontal, 

 terminating in a bifurcation ; between the first and second folds 

 occurs a slight denticle, elongated horizontally ; 3° and 4°, two 

 similar folds, but only their anterior portion nearly horizontal, 

 their posterior portion deflexed obliquely downwards, with an 

 obtuse angle; 5°, a fold similar to the preceding two, but shorter ; 

 and 6°, a short, slight, nearly horizontal fold, close to the lower 

 suture; a low, transverse, callous ridge connects these folds. 



Major diam. 12, minor 11 mm. ; alt. 5 mm. 



Hab. — Miri Hills, Upper Assam [Oijicers, Miri Mission). 



Type No. 3205 Brit. Mus. 



The raised lyrae differentiate Plectopylis miriensis from all 

 other known species of the genus. These appear only on the 

 post-embryonic 3| whorls, the earlier ones of which are furnished 

 on the upper side with 4 lyrae, but about the beginning of the 

 last half of the penultimate whorl their number gradually in- 

 creases to 5. Owing to the fact that the inner one of these is at 

 some distance from the suture, the latter appears channelled, the 

 same condition obtaining as regards the suture in the umbilicus. 

 On the outer and the lower side of the whorls — from the upper 

 angulation to the umbilical suture — I have counted 21 such lyrae, 

 making 26 in all. 



The species has its nearest ally in P. pinacis from Darjeeling, 

 but the latter is dark brown and larger and is only striated spir- 

 ally, the spirals being also more crowded, while at the sides they 

 are almost obsolete. P. pinacis, moreover, is angulated around 

 the umbilicus, which is more open and perspective than in its 

 ally. In their barriers the two species are also closely related, 

 but the parietal transverse plate in P. miriensis has no posterior 

 support at its upper extremity, and the anterior support is ob- 

 liquely deflexed downwards at an acute angle, while in P. pinacis 

 this support is much shorter and directed upwards. In the 

 palatal armature likewise considerable differences are met with, 

 the second fold in pinacis being straight, instead of curving down- 

 wards in the middle. The latter species, moreover, does not 

 possess the transverse callous ridge connecting the horizontal and 

 oblique folds in P. miriensis, a feature it shares with P.muspratti, 

 and a few other species which, however, belong to a different 

 section. Finally, the additional median denticle between the first 

 and the second fold is lacking in pinacis, it is, in fact, a character 

 which I have not observed in any other species of Plectopylis. 



