140 



CEYLON PEARL OYSTER REPORT. 



Fig. 1. 



Fig. 1b. 



Fig. 



Fig. 3. 



Figs. 1, 1a, 1b. 



Dichelaspis pdlucida, Darwin. Fig. 2. Dichelaspis equina, Lanchester. 



Fig. 3. Dichelaspis warwickii (Gray) After Darwin. 



D. equina is the commonest member of its family found attached to crabs from 

 shallow water off Ceylon and the east coast of India.* It occurs both on species 

 which swim near the surface and on those which crawl on the bottom, and is 

 occasionally taken on sea-snakes, though less frequently than D. pellucida. On 

 the crabs it does not confine itself to any particular part of the body. The 

 following is a list of the Crustaceans on which I have found it : Neptunus gladiator, 

 N. 2Klagicus, Scijlla serrata, Doelea ovis, Egeria sp., Arcania septemspinosa, and 

 Dorippe dorsipes. 



Dichelaspis pellucida, Darwin (1). 



I have recently examined a considerable number of specimens of this species from 

 the coasts of Burma and Ceylon. They vary considerably not only in size and 

 in the shape of the valves, but also as regards the degree of calcification of these 

 structures and of transparency of the membrane, as well as the form and the relative 

 proportions of the peduncle and capitulum. Figs. 1, lA, and IB show the outline 

 of some specimens in the Indian Museum. Transparency, outline and proportions 

 probably alter considerably if specimens are not carefully preserved. It seems not 

 improbable that Darwin's JD. grayii and D. pellucida are identical, in which case 

 the former name would have precedence, as the description is printed before that 

 of D. pellucida. I have no doubt that Gruvel's D. lepadiformis also belongs 

 to the same species, although I separated it in my recent list of the Indian 

 Lepadidre (13). His account of the penis (12), which is the most striking feature 

 of the form, does not differ very materially from Hoek's description of that of 

 D. pellucida (4), to which description no reference is given in Gruvel's monograph. 

 Judging from specimens I have examined, the exact outline of the penis in the more 



* Since this was written specimens have been received at the Indian Museum from the Persian Gulf. 



April 30, 1906. 



