1888.] 



AUSTRALIAN CLADOCEEA. 



Gen. Ilyocryptus, G. 0. Sars. 



5. Ilyocryptus longiremis, n. sp. 



(PL 4). 



Specific Characters. — Carapace as seen laterally subtrian- 

 gular, considerably dilated posteriorly, with the anterior part of 

 the dorsal side in adult females strongly vaulted, almost gib- 

 bous, inferior and posterior edges of valves passing into each 

 other by an even but very prominent curve, dorsal edge ter- 

 minating posteriorly as an obtuse angle. Head very small, more or 

 less decumbent, as seen laterally triangular in form, terminating 

 anteriorly with a sharp corner; fornices rather prominent and 

 meeting in front. Carapace in old specimens exhibiting numer- 

 ous concentric lines of growth, caused by the imperfect exuva- 

 tion of the shell. Free edges of valves fringed with a dense 

 series of ciliated setae, those on the posterior edges becoming 

 shorter and having each at some distance from the base a single 

 strong secondary spine. Eye in female considerably remote from 

 the front, in male somewhat larger and nearer the anterior cor- 

 ner. Ocellus considerably smaller than the eye. Antennulae of 

 female very narrow, cylindrical, of male distinctly dilated in 

 the middle and bearing anteriorly a slender bristle. Antennas 

 very powerful and more elongate, than in other known species, 

 natatory setae excessively long, especially the terminal ones, but 

 not ciliated. Tail very large, lamellar, dorsal edge sinuated 

 above the middle, outer part armed with a double row of small 

 denticles (about 16 in each row), and also with a lateral row of 

 about 8 slender spines, the upmost somewhat remote from the 

 others; upper part of dorsal edge convex, with a single row of 

 about 8 strong spines; caudal claws elongate, with 2 very small 

 and hair-like secondary denticles at the base; 4 minute denticles 

 on either side between the caudal claws and the lateral series 

 of spines. Colour orange, in old specimens bright reddish. Length 

 of adult female reaching 1.40 mm. 



Remarks. — I was at first in some doubt, whether this form 

 perhaps might prove identical with the species recently described 



Vid-Selsk. Forh. 1888. No. 7. 3 



