1916.] J. HORNELL: Indian Varieties and Races of Turbinella. si 
periostracum. Shells here grow to 7 inches in length by 4'5 inches in diameter, giving 
a ratio of length to breadth of 1:555, whereas I have seldom seen Tirupalagudi shells 
more than 5 x 3°15 inches—a ratio of 1'587. Typical shells are shown on Plate X, 
Be. 6; and Pl: XI, fier | 
A marked characteristic of many of these shells is a coating of some foreign 
organic substance upon the periostracum. This extraneous skin gives the shells a 
dark, blotchy, and dirty appearance. It appeats to be due to the presence of a 
crusting hydroid allied to Hydractinia, but as I have not yet examined it in the live 
condition, I cannot say positively what it is. 
This form also crosses to Ceylon, where, among the many islands around Jaffna, 
conditions are so diverse that merchants distinguish quite a number of trade varieties, 
separated by differences in weight, size, and shape (Pl. XI, fig. 8). These approxi- 
mate more or less to races (a) and {b) but one may be described separately as worthy 
of remark. This is :— 
(c) The Nayinativu race.—These shells, fished off the island of Nayinativu, are 
remarkable for the large size and heavy weight attained, ranging up to 6°9 x 4°25 
inches (breadth in length, 1°62) with a weight of 2 lb. 2 oz. (Nos. I and 7 in fig. 8, 
Plate XI}. The periostracum is thick, the first and the second or shoulder nodal 
row usually fairly well developed. This form approaches closely to short, stout, aged 
examples of var. acuta and goes far to prove the specific identity of the obtusa and 
acuta forms. I should also remark that similar approximation to the acuta form is 
also to be found amongst the largest sizes of the Coromandel race. Among these we 
get many shells closely similar to those from Nayinativu, with others having the spire 
greatly telescoped and distinctly top-shaped in form. 
Taken generally the larger the shell grows, the less emphasized are the varietal 
differences, so that when the largest specimens of obtwsa and acuta are ranged along- 
side one another, it is impossible to draw any definite line of demarcation between 
them. = | 
On the other hand, the medium sizes, from 3 to 44 inches in length, show the 
greatest amount of divergence, and it is never impossible to separate an average group 
of obtusa from one of acuta, though selected individuals can usually be found to bridge 
the interval. 
2. Variety acuta, var. nov. 
Next in numerical and commercial importance to variety obtusa comes the 
elegant form which I distinguish under the above name. Its habitat marches at the 
head of the Gulf of Mannar with that of the type. It is to be noted particularly that 
it passes northward out of the Gulf at two points, the first at Pamban Pass beyond 
which it spreads fan-like east and west, and the second through the channels of 
Adam’s Bridge, whence it passes west along the whole of the N. E. and N. coasts 
of Rameswaram Island and eastward to the north coast of Mannar Island in the 
vicinity of Talaimannar. To the south, on the Ceylon side, it spreads over the Pearl 
Banks in fair numbers as far south at least as Dutch Bay, and then in diminishing 
