114 HELIX. 



thickened and revolute, interior usually more or less constricted by 

 lamellar teeth, situated far within, but visible through the wall of 

 the shell when held against the light, parietal wall generally with 

 lamellae, one of which is large and visible, the others deep-seated. 



Subsection I. ATOPA (restricted). 



Parietal lamellae entering, simple, aperture sometimes entirely 



unarmed. H. ERRONEA, Albers. 



So. Asiatic. 

 Gorilla, H. and A. Adams, 1855, is a synonym. 



Subsection II. PLECTOPYLIS, Benson, 1860. 



Aperture with one or more deep seated perpendicular lamellae on 

 the parietal wall, in addition to the entering parietal and palatal 



lamellae. H. PLECTOSTOMA, Benson. 



India, China. 



Major Godwin Austen, whose synopsis of the Indian species is 

 followed in these pages remarks (Zool. Proc., 611, 1874) : 



" It seems difficult to account for the use of the extremely con- 

 tracted form of the last whorl, as seen so largely and intricately 

 developed in this group of the Helicidae." 



"When breaking up a number of shells to expose the barriers, 

 and ascertain if their characters were constant, I was greatly inter- 

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

 become fixed between the sets of teeth ; it has occurred to me that 

 this is a probable solution, and perhaps one of the uses which the 

 barriers serve, and to this end have been developed." 



" Insect life swarms in the forests where the shells are found ; 

 and it is quite possible that certain kinds of beetles, ants, or even 

 leeches, prey upon the mollusca, and that those possessing such bars 

 to their predatory visits, supplemented by the mucous secretion 

 which the animal could at once exude, would have the best chance 

 of surviving." 



As stated above, it is necessary to break away the wall of the 

 shell to discover the structure of the lamellae, the strong entering 

 parietal one being alone visible from the mouth. 



Group V. ANCHISTOMA, Ads., 1855. 



Section GONOSTOMA, Held, 1837. 

 Subsection DREPANOSTOMA, Porro, 1836. 



H. NAUTILIFORMIS, Porro. PL 23, figs. 63-65. 



Perspectively umbilicated, corneous, hispid, spire immersed ; 

 whorls 5, narrow, scarcely conspicuous at first, the last whorl large, 



