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. apevta 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 Aurivilhus'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. a-perta, 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 hsematoxylin. 



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. hullata 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 



