124 
Memoirs of the Indian Museum. 
[VoL. II, 
scutum was somewhat L“Shaped, but the angle at which the two branches met was 
rounded off ; the aperture was vertical and broadly patent above; the capitulum was 
pointed at the apex, without a lobe. 
(5) D. cuneata differed from D. aperta in that the scutum was divided a little 
above the point at which the two branches met and the aperture was not so patent. 
Differences in the length of the peduncle I have not noticed, as this is a variable 
feature in all the species of the genus I have examined. The .shape of the capitulum 
in species so soft and so liable to be distorted by alcohol as D. sinuata cannot be 
regarded as a reliable character on which to found specific diagnosis and is, as a 
matter of fact, extremely variable even in well-preserved specimens which otherwise 
resemble one another. The same is true of the exact direction of the aperture, the 
shape of which can apparently be altered at will by the living animal. As regards 
the latter point, moreover, all Aurivillius’s figures seem to me to be incorrect in one 
particular, viz., in the position assigned to the lower extremity of the opening. In 
his representations of D. aperta, D. cuneata and D. hullata this point is shown as 
considerably above the inferior extremity of the scuta, while in that of D. angulata 
the whole of the aperture appears to be confined to the space included between the 
scuta in their inferior half. In all the individuals I have examined it is possible, 
although often with difficulty, to see that the aperture extends from a point between 
the bases of the scuta nearly to the upper extremity of the capitulum. Frequently 
the lips are closely adpressed in the lower half of the opening , and occasionally this is 
the case both above and below the middle third. In transparent specimens it is 
difficult to see the separation between the lips when they are pressed together, but 
no such difficulty exists as regards specimens which are naturally somewhat opaque 
or have been stained by some suitable reagent such as borax carmine or hæmatoxylin. 
The translucency of the capitulum and peduncle is a variable feature in this 
species as in many others, and so also is the development of chitinous points on the 
cuticle. Some individuals are quite transparent even after preservation in spirit, so 
that it is possible to examine their structure under the microscope without treating 
them with any special reagent. Others are much more opaque. >Some have their 
whole external surface covered with small round chitinous tubercles of a deep yellow 
colour, while in others these points, although probably never altogether absent, can 
only be detected with great difficulty. The general opacity or translucency of the 
integument does not depend upon the degree of development of these tubercles, but 
is due to something inherent in the structure of the mantle and other parts of the 
animal. 
The degree to which the valves are developed in different individuals or varieties 
of the species, is a character not devoid of a certain kind of consistency although by 
no means reliable as a means of diagnosis. My chief reason for considering the form 
I described as Dichelaspis transversa distinct from Aurivillius’s D. buHata was the fact 
that all the specimens I had examined at the time the former was described possessed 
a Carina. In the large series of specimens now before me, however, there are indivi- 
duals with no Carina, others in which a minute, needle-shaped calcareous body can 
