28S Transactions of the Society. 



round the disk recalls the dorsal cephalic ring of D. atkinsoni var. 

 bolicari; in fact young individuals very closely resemble the 

 young of D. atkinsoni. M. Richard does not figure the post- 

 abdomen of the male separately, and his figure of the whole 

 animal (plate IX. fig. 9) is misleading. The post-abdomen of the 

 male does not, in fact, differ materially in shape from that 

 of the female (plate IX. fig. 10), but there are fewer and more 

 irregular denticles along the dorsal border and a group of spinules 

 on the small papilla on which the vas deferens opens. 



Daphnia magna Strauss. — This species was common in Biskra 

 in irrigation pools and in some of the larger ponds. It was also 

 found in highly saline water by Lake Sedjouma and at Sidi 

 Athman and Rades. The specimens from water of high density 

 showed no differences from the type resembling the varieties found 

 by Schmankewitsch in similar situations. 



Simosa vctwla (O.F.M.). — Apparently rather a rare species in 

 Algeria and Tunisia. A few individuals were found in ponds in 

 the Jardin d'Essai in Algiers and at Oued Tindja near Tunis. 



Ceriodaphnia reticulata Jur. — Found only in an irrigation tank 

 in the Jardin d'Essai in Algiers, and in a pond near Tunis. 



Ceriodaphnia dubia Eichard. — A species of Ceriodaphnia was 

 found rather commonly both at Biskra and in Tunisia, which I 

 rather doubtfully identify with C. dubia Richard. With regard 

 to general form, shape of the head, fornix, antennas, and reticula- 

 tion of the shell and head, the agreement is complete. The shape 

 of the post-abdomen varies somewhat according to the degree of 

 contraction of the specimen, but in its extended condition it has a 

 tapering form as shown in M. Richard's figure. The claws are 

 long and very distinctly ciliated, the cilia arranged in a proximal 

 and a distal series. The teeth of the dorsal surface are ten or 

 eleven in number and are short, those in the middle of the series 

 being slightly the longest. The only conspicuous point of differ- 

 ence is the presence in some specimens of a very long dorsal 

 process closing the brood-chamber. M. Richard says that in most 

 specimens there is a " prolongement conique court faisant saillie 

 dans la cavite incubatrice," and in many of my adult specimens 

 the same condition is found ; there appears to be great variability 

 in the length of this process. There is, however, a great difference 

 between the ephippium in my specimens and that of C. dubia as 



EXPLANATION OF PLATE XL 



Fig. 17. — Macrothrix hirsuticomis Norm. & Br. First antenna of male, x 260. 

 ,, 18. — Ditto. Post-abdomen of male, x 260. 

 ,, 19. — Alona elegans Kurz. Part of shell of ephippial female, showing line of 



fracture, x 440. 

 ,, 20. — Chydorus letoiirneuxi Rich. Male, x 260. 

 ,, 21. — Ditto. First antenna of male, x 440. 

 „ 22. — Ditto. Female, portion of shell margin, x 1050. 

 ,, 23. — Ditto. Ephippial female, x 120. 



