MOLLTJSCA OF INDIA. 197 



refers to ' coll. Skinner.' As this collection passed into the hands 

 of Miss Linter, I inquired if she possessed the species ; she kindly 

 informed me that no traee of it could be found in the catalogue of 

 the collection. Recently I have had from Mr. Collett two very 

 interesting specimens, in good condition, which I refer to this 

 species. Provided we assume that when Pfeiffer speaks of ' carinis 

 duahus ' one may be almost in the suture, they agree fairly well 

 with his diagnosis, save that on examining the base under a lens 

 I find palatal and parietal armature of the Plectopylis (Si/l-esia) 

 type. It may well be, however, that if his specimens were not in 

 good condition this would not be apparent I think, there- 

 fore, that it is wiser to refer these shells to PfeifFer's species, which 

 must be regarded as a Si/kesia, than to describe them as new." 



It was in April 1897 that Mr. Gude, with his accumulated know- 

 ledge of the shells of Plectop>jlis, came to the conclusion it was 

 necessary to form a subsection of the genus on two species " cha- 

 racterized by a thin and transparent shell with straight acute edges," 

 viz, clathratula from Ceylon and retifera from India. In this ho 

 was, I consider, justified on shell-character, for these species are 

 very distinct from typical Plectopylis ; he writes : — " I propose the 

 name Aastenia in honour of Lt.-Colonel Godwin-Austen, who has 

 contributed so largely to our knowledge of the genus." In May 

 1897, in ' Science Gossip,' vol. iii. p. 332, he amended this : — - 

 " Mr, E. E,. Sykes and others have drawn my attention to the fact 

 that the name Austenia proposed by me for a section of PlectojJijUs 

 (ante, p. .300) is pre-occupied. Under these circumstances it is 

 iiecessary to re-name the section, and I therefore propose the name 

 Sifkesia, in honour of Mr. Sykes, who was the first to point out this 

 fact." 



Mr. Gude, in his classification of the genus Plectopylis, ' Science 

 Gossip,' vol. vi, Nov. 1899, p. 175, divides it into seven sections, 

 the last of which is SyJcesia. I give his key to the section : — 



" VII. Section Sykesia. 



A. One transverse parietal fold. 



a. Notched about the middle, a short support posteriorly above. 

 Ceylon. 

 a. Umbilicus wide, ribs and lyrae prominent. . clathratula. 

 ft. Umbilicus narrower, ribs and lyrae obsolete. . v. compressa. 

 h. Not notched. 



a. Straight, without support ; umbilicus still narrower. 



Habitat India, clathratuloides. 

 ft. Sinuous, with a short support anteriorly above ; umbilicus 

 still narrower Habitat India, retifera. 



B. Two transverse parietal plates. 



a. Shell flattened ; no fold below umbilical angulation; umbilicus 



still narrower Habitat Ceylon, caliyijiosa. 



b. Shell conoid, with a double fringe of curved hairs ; a horizontal 



fold below umbilical angulation ; umbilicus still narrower. 



Narrowest of all Habitat Ceylon, hiciliata.'" 



s 2 



