300 Transactions of the Society. 



Poppclla guemei Richard. — A few specimens of this peculiar 

 species were found in a marshy lake by the outflow of the Lake 

 Garaa Achkel at Oued Tindja. The water was perfectly fresh. 



The species was found by M. Richard in a fresh-water canal in 

 southern France, but has also been recorded by Sars from the 

 Caspian Sea, and by Van Douwe from Transca.mia and Turkestan. 

 Its distribution is therefore peculiar both geographically and bio- 

 logically, since it occurs both in fresh-water and also in water of 

 very high salinity (Bay of Karabugas). 



Professor Sars has stated his opinion that the large double- 

 toothed plate on the posterior face of the second joint of the fifth 

 foot in the female figured by Richard is nothing more than the 

 terminal part of the newly-formed leg as seen just before the moult. 

 Van Douwe has, however, fully confirmed Richard's description by 

 the examination of Transcaspian specimens, and my own show the 

 existence of the toothed plate as clearly as possible. Viewing the 

 anterior face of the leg, this plate, as seen through the leg, has 

 a remarkably close resemblance to the third joint of the latter, 

 and might easily give rise to error. It is, of course, possible that 

 the Caspian form is a distinct species. 



A small anatomical point has not been mentioned by either 

 Sars or Van Douwe. On'the inner face of the twenty-third and 

 twenty-fourth joints of the antenna in the female, there is a very 

 delicate hyaline lamella, or rather " stiftchensaum," since its 

 delicate striation indicates that it is composed of excessively fine 

 cilia. This lamella is supported distally by a peculiar, highly 

 refringent, curved rod of chitin (plate XIV. fig. 46). 



Conclusion. 



Much work has already been done on the fresh-water Crus- 

 tacea of North Africa, particularly by M. Richard and Professor 

 Sars, who have worked largely on material supplied by M. 

 Chevreux. Compared with those of Algeria, the Crustacea of 

 Tunisia have been somewhat neglected, but my own collections, 

 though I spent but a few days in that country, are sufficient to 

 show that the fauna of the coast region, or Tell, is very rich and 

 will repay closer investigation. I think it worth while to give 

 here what I believe to be a complete list of the species hitherto 

 recorded from Algeria and Tunisia. I have included in it all the 

 species found by me, and have indicated roughly the distribution 

 of each one. 



