334 MR. ROBERT GURNEY ON 



All belong to the same species, and that, in my opinion, is 

 D. excisiom, since they agree in all essential respects with Sars's 

 description, though somewhat smaller than the size given by him. 

 It is i-emarkable that the only species of Diaphanosoma recorded 

 from Ce3'lon is D. singcdensis Daday, which was found by Apstein 

 to be common in the Colombo Lake from January to September. 

 All the specimens that I have examined have the ventral shell- 

 margin markedly reflexed, and cannot possibly be referred to 

 D. sivgalensis. It is possible that there is a seasonal alternation 

 of the two forms. • 



Daphnia lumholtzi Sars, 



A few young specimens were taken in a tank at Kandy. 



Ceriodaphnia rigaudt Richard. 



Peradeniya pond ; Colombo Lake ; Mahintele ; Anuradlipura ; 

 Kandy tank. 



Ceriodaphnia cornuta Sars. 



Kandy, in a pond by Lady Horton's Drive and in the tank. 



Daday (1898) has expressed, and still maintains, the opinion 

 that C. cornuta and C. rigaudi are merely extreme forms of 

 one species, and a careful examination of the specimens at my 

 disposal gives much support to such a view. The presence or 

 absence of a head-spine is, in my specimens, usually correlated 

 with the possession of a posterior shell-spine, which is slightly 

 bifurcated or simple respectively; but not only do both rigaudi 

 and cornuta forms occur together in the same collections, but 

 also individuals are found which it is almost impossible to assign 

 to one or the other. The head-spine may be so small as to be 

 detected with great difficulty, and the shell-spine may show but 

 the faintest trace of bifurcation. It appears to me that the 

 rigaudi form may occur alone, but that wherever (in Ceylon) 

 C. cornuta occurs, there also are found a small number of 

 individuals which, in the lack of its distinctive characters, 

 approach C. rigaudi. One may conclude that the species may 

 be in fact distinct, but that G. cornuta is very variable and 

 may approach C. rigaudi in appearance. The cornuta form 

 described by Stingelin from Java, and having a double head- 

 spine, must be regarded as merely a, variety of the species, since 

 Daday (1910) has found specimens with double head-spines 

 together with others of the typical form in Victoria Nyanza. 



MoiNA DUBiA Richard. 



Kandy; Mahintele; Anuradhpura. Common. 



I take this opportunity of correcting aii error in my figure of 

 this species recently published (1911, pl.ii. fig. 1). In this figure 

 the reticulations of the ephippium are shown strongly marked 

 over the egg-space, whereas, though a veiy faint reticulation can 

 sometimes be detected, the egg-space usually appears quite 



