Mr. W. H. Benson on Plectopylis. 247 



vertical! simplici antice lamellam 1 inferiorem elongatiusculam 

 emittente, lamella superiore valde elongata aperturse laminam pa- 

 rietalem non omnino attingente, plica basali obsoleta ; plicis pala- 

 talibus intrantibus 6, tribus superioribus et basali elongatis sinu- 

 osis, quarta et quinta brevibus, postice plicis obliquis distinctis 

 munitis. 



This form occurs at Phye-than, in the Tenasserim Valley. It 

 exhibits an approach to the next section in some of the palatal 

 plaits. 



5. Helix plectostoma, B. 



Janua pliciformi fauciali prima minime profunda, ab apertura partim 

 apparente; lamina 1 parietali vertical! simplici, lamellis uullis 

 munita, plica basali brevi ; plicis sex palatalibus, superiore basali- 

 que simplicibus, secunda vix duplicata, tertia, quarta quintaque 

 postice plica obliqua munitis. 



This form inhabits Darjiling and the Khasia Hills. 



6. Helix Pinacis, B. 

 (Annals Nat. Hist. April 1859, p. 268.) 



Janua pliciformi fauciali prima profundiuscula, ab apertura vix appa- 

 rente. Lamina et plica basali ut in specie antecedente, plica basali 

 nonnunquam obsoleta; plicis sex palatalibus, prima et secunda 

 supernis plus minusve simplicibus, tertia vix duplicata, quarta, 

 quinta basalique duplicatis, hujus plica secunda ad latus concur- 

 rente, nee postica. 



It differs from H. plectostoma in the formation of the chief 

 palatal plaits, and in having a supplementary parallel basal fold. 



This species is found rarely near Darjiling. A minute variety 

 occurs among Mr. W. T. Blanford's specimens of H. plectostoma , 

 3 i to 4 \ millimetres in the larger diameter. 



There appears to be a regular gradation from H. Achatina to 

 H. Pinacis, through Cyclaspis, Leiophis, refuga, and plectostoma, 

 each species presenting peculiarities in the details of the pylaic 

 plication. 



Dr. L. Pfeiffer attributes only three palatal plates to Helix 

 erronea, Albers. On filing into the shell behind the lamellae, a 

 fourth is found, as well as in H. Rivolii, Desh. The arrange- 

 ment of the lamellae differs in the two species. 



On a close examination of the little Cingalese Helix clathra- 

 tula, Pfr. (H. Puteolus,~B.), a sparsely toothed lamellation becomes 

 apparent internally : it is seen through the transparent lower 

 side in two parallel lines, as many as six teeth occurring in a 

 group ; occasionally some are visible from the aperture. Pfeiffer 

 refers this shell to Patula. 

 Cheltenham, March 1, 1860. 



