BELONGING TO DAJHNlA AND OTHER ALLIED GENEI14.. 229 



somewhat flattened in front, its lower margin forming a long 

 sinuated curve, and ending in a slender, subacuminate, conical 

 beak, the posterior margin of which has a pouting prominence 

 (fig. 15). Dorsal margin of the valves gently and evenly arcuate, 

 ventral more evenly arched and slightly protuberant just at the 

 base of the terminal spine ; posterior extremity narrowed, ending 

 in a long, slender spine which rises above the middle line and 

 projects nearly straight backwards. The abdominal processes 

 are short and separate (fig. 16), terminal unguis of the post- 

 abdomen more or less pigmented, feebly bidentate on the convex 

 edge, and bearing a continuous row of very fine hairs on its con- 

 cavity (fig. 17). Pre-anal spines 12-15 in number, increasing 

 gradually in length from before backwards (fig. 16). The an- 

 tennal setae are as usual biarticulate, and each seta has, a little 

 beyond the median joint, a conspicuous black pigment-fleck 

 (fig. 18). Length, exclusive of the spine, about 1"55 mm. The 

 ephippial female is rather shorter in proportion to its height, 

 and has a strongly angulated dorsal margin (fig. 19). 



Male. — The male is smaller than the female, subrhomboidal 

 in outline, with nearly straight dorsal and ventral margins, the 

 terminal spine long, projected slightly upwards and springing 

 from the postero-dorsal angle (fig. 11). The head is without a 

 beak and is deeply sinuated beneath. Antennules truncated, 

 bearing six apical setae, all of which are very delicate, four being 

 very short, the other two about twice as loug, but not prehensile 

 (fig. 12). Abdominal processes rudimentary; pre-anal spines 

 about six or eight in number (fig. 13). Length, 1 mm. 



In the surface waters of small lakes and tarns Daphnia longi- 

 spina is probably the most abundant species of the genus, occur- 

 ring not only as a pelagic form, but likewise very plentifully 

 amongst shore weeds. But it is by no means confined to such 

 localities, small pools and ponds often producing it in abundance. 

 Specimens from different places vary considerably in minor points, 

 and on these variations many so-called species have been founded. 

 Professor Gr. 0. Sars'''' now reckons as mere varieties of longispina 



* Oversigt af Norges Orustaceer, med forelobige Bemaarkniiiger over de nye eller 

 mindre bekjendte Arter, p. 19 (1S90). 



