MOLLUSCA OF INDIA. 



203 



while external characters taken in a wide sense apply to a multi- 

 tude of very different genera. The relationship of Plectopylis and 

 Gorilla with OpMor/yra, Pohjgijra, and Gonostoma (North and South 

 America) is, in my opinion, so remote as to be not worth further 

 consideration. The odontognathous jaw of these last is sufficient 

 to show this, to say nothing of other equally important differences. 

 Clausilia can be traced back to the Eocene, but geological evidence 

 points to the great probability of Corilla having been an inhabitant 

 of Southern India in the Middle and Upper Cretaceous Periods. 



Anchistoma cretaceum, Stol. (a fairly common species), A. arria- 

 loorensis, Stol., and A. arcotense, Stol. (only a single specimen of these 

 two last), are extremely like Corilla and Flectojiylis, particularly the 

 last-named species, with its closely mauy-whorled and flattened 

 upperside {vide pi. i., ' Memoirs Geol. Survey of India : Palseonto- 

 logia Indica,' " Cretaceous Kocks of Southern India," by Ferdinand 

 Stoliczka). The similarity is enhanced by the presence of internal 

 teeth and thin fold-like plaits ; if a large series of specimens could 

 be obtained, closer examination of the internal barriers would yield 

 valuable results. Stoliczka says (p. 7) :— " It can scarcely be 

 doubted that a careful search in these deposits (Arialur Group) 

 formed in shallow waters (Mem. Geol. Surv. India, vol. iv. pt. 1, 

 p. 163) would largely reward the observer by adding to the number 

 of the Cretaceous land — and probably freshwater — shells also." 



When Stoliczka wrote this (1867) he had not entered on the 

 study of the anatomy of the Indian land-sheUs ; he followed the 

 classification of H. & A. Adams and Benson, and placed these 

 fossil forms in Anchistoma ; but he makes it quite clear, on p. 9, 

 that they were in general form next to the Indian Plectopiilis, 

 which, in Adams' ' Genera of Recent Mollusca,' is included with 

 some subgenera in the subgenus Corilla, H. & A. Adams, = 

 Atopa, Albers, of the genus AncMstoraa, Klein. Stoliczka also 

 observed at this date how undefined the above subgenera are ; he 

 says (p. 9) : — " To make these separations of real classificatory 

 value, it is absolutely necessary that they be based upon the 

 examination of the animals as well as the shells, so as to be certain 

 whether the respective organs can in any way be depended upon as 

 to their constancy." A work he commenced, did some admirable 

 work in, but unfortunately was not spared to complete. 



Plectoptlis pinacis, Benson. (Plate CXIV. figs. 2-2 d.) 



Helix pinacis, A. M. N. H. ser. 3, 1859, vol. iii. p. 268 : Pfr. Mon. 

 Hel. vol. V. p. 417 ; Hanley, Conch. Ind. p. 7, pi. xiii. fig. 5, 

 p. 36, pi. Ixxxiv. figs. 1-4. 



Plectopylis pinacis, Theob. Suppl. Cat. p. 25 ; Nevill, Hand-list, 

 i. p. 71 ; Godwin-Austen, P. Z. S. 1874, p. 612, pi. Ixxiv. fig. 1 

 (parietal, vertical lamina of) ; Gude, Sci. Gossip, 1897, vol. iii. 

 p. 206 (armature). 



Helix {Gorilla) pettos, Von Martens, Malakoz. Bljitt. vol. xv. 1868, 

 p. 158. 



