Oil Fresh-water Crustacea. By Rohert Gfumey. 295 



salt water only by Lake Sedjouma, at Oumach, Rades, and El 

 Ariana. M. Richard suggests that the presence of this and other 

 species of Harpacticids in the Algerian Sahara may be adduced as 

 evidence of the existence of a quaternary inland sea. On the 

 other hand these minute Crustacea are so easily dispersed that it 

 is more reasonable to suppose that these species have recently 

 colonised the inland waters which they have found suitable by 

 reason of their high salinity. There appears to be overwhelming 

 evidence that the Algerian Sahara has not recently been covered 

 by the sea, but rather that there was, in late Pliocene and Quater- 

 nary times, a Lacustrine period in which rivers and great fresh- 

 water lakes existed in the Sahara. The chotts are the sunken 

 relics of these lakes, the water of which has become progressively 

 Salter. With the increase of salinity of the Saharan lakes they 

 became suitable for the colonisation of brackish species, such as 

 Cardium edule and certain Harpacticids. Cardium has now dis- 

 appeared, since the water of the chotts is too salt for it. Had the 

 Harpacticids been relics of an ancient sea it is probable that they 

 would now be represented by species peculiar to the district, 

 whereas the only species not yet found elsewhere is Mesochra 

 lyhica Blanch, and Rich. 



Diaptomus incrassatus Sars. — This species was found in some 

 numbers in pools and ditches at Sidi Athman and Oued Tindja 

 near Tunis. Through the kindness of Canon Norman I have been 

 able to compare my specimens with co-types sent to him by 

 Prof. Sars, so that I feel no doubt as to their identity. The only 

 difference of any importance that can be detected lies in the form 

 of the rostral filaments. In specimens from Mongolia these are 

 long and tapering, whereas in mine they are short, broad at the 

 base, and abruptly contracted distally into fine points. In my 

 specimens the genital segment is slightly broader and has a 

 minute spine on either sid^. 



The species has not been found hitherto elsewhere than in 

 Central Asia, where it appears to be widely distributed and 

 tolerant of a rather high salinity. Its occurrence in Tunisia is 

 comparable to the occurrence in North Africa of Hemilepistus 

 reaumuri, which belongs to a genus of Isopods confined, with one 

 other exception, to Central Asia. 



Diaptomus numidicus sp. n.— Body rather slender, the greatest 

 width near the middle of the thorax (plate XII. fig. 31). Last 

 segment of the thorax in the female expanded into sharply pointed 

 lobes. Abdomen of the female composed of three segments ; the 

 genital segment more than twice as long as the last two combined, 

 not greatly expanded, and with a small spine on either side 

 (plate XII. fig. 28). In the male the fourth segment is slightly 

 asymmetrical, overlapping the fifth segment on the right side. 



