1865.] Contributions to Vadium Malacology. 91 



approaching each other, and united by a callus. Major diameter 18, 

 minor 15 J, axis 8 millemetres. 



Habitat — Mya Leit Doung. Ava. 



This differs from all allied forms in its much coarser flexuous sculp- 

 ture, and from most of them by its blunt angulation at the periphery. 

 It is also, so far as I know, the largest form, belonging to this group, 

 which occurs in Burma.* 



H. tapeina is said by Mr. Benson to be distinguished from rotatoria, 

 amongst other characters, by the greater regularity of the sculpture in 

 the former shell, which contrasts with the irregularly flexuous stria- 

 tion of the latter, f I have never seen a typical specimen of H. rota- 

 toria, which was originally described from Java, but Mr. Benson has 

 identified with it a shell which abounds at Thayet Myo, Frome and 

 Akoutonng, and a variety of which, with a flat spire, Mr. Theobald 

 has called H. Ahoutongensis. Of H. tapeina I possess specimens collected 

 by Mr. Theobald at the original locality, the Khasi hills. These 

 have a slightly more regular sculpture, an angulate periphery instead 

 of the sharp compressed keel of the Pegu form, and a rounder mouth, 

 but the spire is sometimes higher, sometimes not, and I can see no 

 distinction in the umbilicus. In all the distinctive characters, varieties 

 shewing gradation, occur in Burma. 



Leaving the craestion of specific distinction, the distribution of 

 varieties of these shells in the Irawady valley, so far as I have searched, 

 is the following. 



On the Shan hills, east of the valley in which lie Mandele, the pre- 

 sent capital of Ava, and the older capitals, Amai-apoora and Ava itself, 

 I found a lenticular sharply keeled form, less swollen beneath, and, in 

 general, higher in the spire than the Akoutonng form of rotatoria, 

 with the sides of the spire straight, not convex. The epidermis, 

 when in good order, and especially in young specimens, is hispid ; the 

 sculpture rather variable, but flexuous. This latter is also the case 

 with the Akoutoung and Thayet Myo form of rotatoria. 



* la a letter received since the above was written, Mr. Benson informs me 

 that H. Pliagrei only differs from his type of H. tapeina in its coarser sculpture. 

 My specimens of the latter shell have a more angulate periphery. 



f In Pfeiffer's Monogr. Helic. Viv., however, H. tapeina (Vol. III. p. 254) is 

 said to be " Subtiliter granulato-striata," while H. rotatoria (Vol. I. p. 203) is 

 described simply as " oblique striata." The former is said to differ from the 

 latter in sculpture, higher spire, narrower umbilicus and rounder aperture. 



