80 



HELICID^E. 



81. Fleet opylis sower by i, Gude. 



Plectopylis soiverbyi, Gude, Science Gossip, N. s. v. 1809, p. 289, 



fig. 93 (shell and armature). 

 Plectopylis (Endothyra) soiverbyi, Gude, op. cit. vi, 1899, p. 148. 



Original description : " Shell sinistral, widely umbilicated, dis- 

 coid, dark corneous, regularly ribbed and radiately distantly 

 plaited, strongly decussated above by spiral ribs, less distinctly 

 so below. Whorls six, narrow, increasing slowly and regularly, 

 somewhat flattened above and rounded below, the last not de- 

 scending in front. ISix or seven spiral ridges, probably, when 

 fresh, bearing rows of hairs, pass round the whole of the body- 

 whorl, the first just above the slightly angular periphery, the 

 others below it. Aperture ear-shaped ; peristome slightly tinted 

 with rosy-pink, scarcely thickened, and a little reflexed ; the 

 upper outer margin a little depressed ; parietal callus slight, 



a * f 



Fig. 30. Plectopylis sowerbyi. 



without raised ridge at the aperture. Umbilicus deep and wide. 

 The parietal armature consists of a strong vertical plate, provided 

 at its lower extremity with a short support anteriorly, and a small 

 denticle posteriorly. The palatal armature is composed of six 

 more or less horizontal folds, the first very slight and short, near 

 the suture, the four next longer and more elevated, a little deflexed 

 posteriorly, the sixth slight and very short." (Gude.} 



Major diam. 7-9, minor 6-25-7*5 mill. ; alt. 3-75-4-75 mill. 



Hob. Assam : Khasi Hills. 



P. sowerbyi is closely allied to P. plectostoma, from which it can 

 at once be distinguished by the following characters : it is flatter, 

 being less raised in the spire ; the umbilicus is more open ; there 

 are only six whorls, the last not descending in front ; the peri- 

 stome is scarcely thickened and not much reflexed, and there is 

 no raised ridge on the parietal callus. In the armature there are 

 also important differences : the vertical parietal plate in P. plecto- 

 stoma gives off from its upper extremity anteriorly a horizontal 



