1916.] J. HORNELL: Indian Varieties and Races of Turbinella. 11i 
conditions, such as surf action, prolonged spells of turbid, mud-laden water, and 
scarcity of food. 
I. Variety obtusa, var. nov. 
Judging the importance of the co-varieties of Turbinella pirum from the numeri- 
cal standpoint, this variety is entitled to first place. It is the form which furnishes 
all but a fraction of the produce of the great fisheries in the north of Ceylon and 
along the Indian Coast of Palk Bay and thence from Point Calimere to Pulicat Lake. 
Out of a total annual production in this region of about 15 lakhs of shells, this form 
contributes 13 lakhs. Its habitat lies entirely northward of a line curving into Palk 
Bay from a point about the middle of the north coast of Mannar Island to another 
on the Indian mainland a few miles west of Pamban (Plate XII). The significance 
of this peculiar line of demarcation will be explained later. 
The characters of this variety fluctuate within considerable limits, from a form 
with a well-marked though short spire to one where it is extremely abbreviated with 
whorls much telescoped. It was the latter which Linnaeus described and which there- 
fore has to be considered the type of the species. To this form I will therefore apply 
the term typica, while for the other extreme the term rapa will be appropriate as it 
was a shell of this form to which Gmelin (1790) applied the specific name rapa. 
The length of both forms compared with varieties acuta, fusus, and comorinensis 
is markedly short in comparison with the breadth, due to (a) an emphatic telescop- 
ing of the whorls of the spire, and to (b) a considerable inflation of the body whorl. 
The former forces the shoulder high up and imparts to the shell a distinctive top- 
shape suggesting stunting, which contrasts sharply with the handsome free growth 
and wide spindle shape of var. acuta. The periostracum in small and medium shells 
is usually thin and weak with a distinct tendency towards smoothness; the spiral 
rows of prominences or nodes and the lines of low periostracal ridges are poorly 
developed, very much less than in acuta; it is seldom that more than a trace remains 
of any except the shoulder nodal row. Young shells of this variety are often richly 
flecked with chestnut spots, but this is a very variable character and many shells 
otherwise exactly similar to the spotted ones are almost or quite spotless, and a 
uniform white. With increasing size spotting tends to be suppressed, and full grown 
shells seldom show the slightest trace of spots. 
Between the two extremes of shape seen in this variety a perfect range of grada- 
tion can be traced, and, although when the extremes be placed side by side their 
differences appear so well-marked as to appear to justify separation, I am unable to 
split it up as these extremes are not localized and intermediate forms are always 
easily found linking them up. 
It is difficult to distinguish any clearly defined local races of this variety ; the 
more important ones are those of (a) Tirupalagudi, (b) the Coromandel Coast, and 
(c) Nayinativu. 
(a) The Tirupalagudi race.—These shells are found off the villages of Tirupalagudi, 
Tondi and Mudirampatnam in the south-west angle of Palk Bay, and come from 
