MOLLUSCA OF INDIA, 31 
is often difficult to be traced. On drier places and on sandstone 
hills the shells become more solid, and are covered with a thin 
horny cuticle; the spiral striation becomes very distinctly dis- 
cernible, and there often appear intermediate strie between the 
four or five stronger spiral ribs. A young specimen of this type 
has been described by Blanford as Nanina culmen. On limestone 
ground the shells become again more solid, often attaining a con- 
siderable thickness, and the specimens also grow to a larger size, 
but the spiral striation occasionally disappears almost entirely on 
the two last whorls. 
«This species is common about Moulmain, though not so much on 
the low land as on limestone hills. 
‘The spiral angle of specimens collected in Burmah varies from 
nearly 70° to 86°. The following table will indicate some of the 
principal variations :— 
Pegu. Moulmain, 
I ON, ae eS 
Number of whorls.. 6 8 4 6, 7 
Larger diameter .. 538 13mm. 7 8 11:2 mm. 
Height of shell.... 55 12 ,, 6:4 (irae 5 ae 
Spiral angle ...... 12.4 280: WOsy pp Sar wear 
Sa ~~ Sees 
culmen. attegia. attegia.” 
I have given this long extract from Stoliczka’s interesting remarks 
on this shell because they show so well how the nature of soil, food, 
and moisture affects within very small areas the form and sculpture 
of the shells of these creatures ; it is these slight changes, gradually 
becoming more permanent, to be extended over larger areas or re- 
maining restricted, that are regarded as local races, or varieties, 
or subspecies, whichever the naturalist likes to call them, and 
which, after all, is quite immaterial to the general result of our ob- 
servations. What we have to show is, how very unequal these 
areas are in size, and how they are distributed; and from this we 
shall find where the boundaries of these changes lie, and thence 
perhaps be able to connect them with the past and present distri- 
bution of land and sea, 
Srrata cutmen, W. Blf. (Plate VIII. fig. 4.) 
Nanina culmen, Contrib. Ind. Mal., J. A.S.B. 1865, p. 72 (section 
Trochomorpha). 
Conulema as =attegia, Bs., Stoliczka, J. A. S. B. 1871, p. 237. 
Sitala as =attegia, Bs,, Theob. Suppl. Cat. p. 20. 
Nanina (Sttala) as=infula, Bs., Nev. Hand-l. p. 33. 
Original description :—*“ Shell very minutely perforated, trochi- 
form, very thin, horny, translucent. Spire conical, apex obtuse, 
suture impressed. Whorls 6, convex above, and ornamented with 
fine raised spiral lines and oblique strive; the last whorl sharply 
keeled at the periphery, not descending, swollen and minutely de- 
cussately striated beneath. Aperture but little oblique, subquad- 
