IIO Memoirs of the Indian Museum.  Vorayae 
results of this study I have found it impossible to draw any hard and fast line 
separating specifically any of the main assemblages. Finally, I arrived at the con- 
clusion that while the two most important forms, which I term obtusa and acuta 
respectively, constitute merely varieties of one species, their varietal characters were 
at no long distant period in process of such permanent fixation that the establish- 
ment of separate species would have been accomplished had not geological changes 
brought the two varieties into close intermingling .before the fixation of specific 
characters was completed. 
Each of the five varieties into which I divide the species, if judged by isolated 
individuals in which are strongly developed the special characteristics and propor- 
tions found in their respective shells, may assuredly be classed without difficulty by 
the closet naturalist as a distinct and wellmarked species. Strangely enough this has 
not happened, for though a considerable number of species have been erroneously 
created through the study of individual shells, all such are based upon the forms and 
local races of the single variety obtusa. Thus 
Voluta gravis, Dillwyn, 
- Turbinella clavata, Schub. and Wagn., 
Turbinella napus, Lamarck, 
are bad species founded upon specimens of the form éypica of T. pirum obtusa, while 
Lamarck’s Turbinella rapa represents form rapa of the same variety and probably 
was based upon a large specimen of this varietal form from the neighbourhood of 
Madras. Certainly the shell figured by Reeve as T. vapa in Vol. IV of his Conchy- 
logia Iconica represents precisely such a shell. 
The first four of the varieties I now propose to define are inhabitants of the 
coastal waters of Ceylon and of Continental India; the fifth (7. pirum fusus) is 
found in the Andaman Islands. 
The following key to the five varieties defines the principal characteristics of 
each :— 
Spire elongate; shell widely ( Shoulder angular, prominent. a var. fusus, Sowerby. 
fusiform. ( ) Profile of whorls in spire con- 
Breadth in length, ( vex, var. acuta, var. nov. 
1:75 to 2. Shoulder rounded, low. ) Profile of whorls in spire 
nearly straight, var. comori- 
nensis, Var. Nov. 
bose; periostracum rough and var. globosa, var. nov. 
thick. 
‘ Spire often very short; shell in- 
| clined to be top-shaped ; very wide 
Spire short; shell either glo- 
bose or top-shaped. 
Breadth in length under 1:75. 
var. obtusa, var. nov. With 
two forms :— 
(a) typica, 
(db) rapa (Gmelin). 
at shoulder. Periostracum thin > 
and little sculptured in small and 
medium-sized shells. 
Spire moderately short; shell glo- . 
I will now discuss in detail the main characters distinguishing these varieties, 
together with those of the shells from different localities, the local variations being 
due in the main to differences in the abundance of food supply, and in the character 
of the environment, particularly in regard to the degree of exposure to unfavourable 
