On Fresh-water Crustacea. By Robert Gvrncy. 291 



fig. 17). They are fringed with cilia, and bear, near the head, two 

 lateral setae. Of these the longest reaches beyond the extremity 

 of the antenna. There are nine terminal sensory rods. The 

 hook of the first pair of legs projects beyond the shell-valves and 

 has three minute tubercles at its extremity. A strong spiniform 

 seta springing from the stem opposes itself to the claw so as to 

 form a sort of chela. The post-abdomen does not differ much from 

 that of the female except that the ventral edge of it in front of the 

 claws projects as a rounded prominence upon which the vas deferens 

 opens (plate XI. fig. 18). 



Ephippial females vary much in size, measuring from ■ 6 mm. 

 to 1 • 3 mm. in length. The ephippial area occupies the greater 

 part of the shell-valve, and differs from the remainder only in its 

 slightly darker colour and in showing no visible reticulation. 

 The surface simply appears to be very dirty. In moulting, the 

 whole of the valve separates from the head. A faint line can be 

 traced, dividing the ephippial area from the ventral reticulated 

 part of the shell, and the shell probably splits eventually along 

 this line. The ephippium contains two or three small oblong 

 resting-eggs. They lie together enveloped in a delicate membrane, 

 which represents the inner layer of the shell, and imbedded in 

 what appears to be cellular tissue. Unfortunately my specimens 

 are not sufficiently well preserved to determine the nature or 

 origin of this tissue. 



Alona elegans Kurz. — Commonly found in Biskra in all the 

 larger ponds which do not rapidly dry up. It was once found 

 also in one of the small pools at the foot of the palms. In 

 Tunisia it occurred at Sidi Athman, Oued Tindja, and Eades, so 

 that it may be considered as a common North African species. 

 Males and ephippial females were found on four occasions, three 

 times in Biskra and once at Sidi Athman. 



The ephippium presents certain features which are of some 

 interest. The ephippium becomes, as is usual, of a deep brown 

 colour, but the surface markings of the shell are not changed, 

 though they are rather more prominent. The outline of the 

 ephippium is marked by an unusually conspicuous " line of weak- 

 ness," composed of large reticulations following the line of the 

 ephippial margin (plate XI. fig. 19). The striations of the 

 ventral part of the shell end abruptly against this line, bending 

 round in the anterior half to meet it more or less at right angles. 

 The ephippium differs from that of most Lynceidse in shape since 

 it includes scarcely any part of the posterior margin of the shell, 

 resembling, in this respect, that of Alonopsis ambigua. In the 

 majority of species only a greater or lesser portion of the ventral 

 margin is thrown off, so that the ephippium includes the greater 

 part of the shell.* 



* Scourfield, 1902. 



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