ON ACANTHOLEBERIS.- a5 
leberts towards the posterior extremity below the point of attach- 
ment of the fifth feet; while in Macrothrix there is no such fold, 
the course of the canal being straight. 
In 1858, Lievin described a second species of the genus; but 
his A. sordida shows such marked points of divergence from the 
type as to make us doubt whether the genus has been founded 
on sufficiently good grounds, and whether it should not rather 
be united with Lathonura, Lilljeborg (=Pasithea, Koch), and 
Macrothriz. A. curvirostris and A. sordida are the only known 
members of the genus, and both these species have now been 
found in Great Britain. 
Acantholeberis curvirostris (Muller). Pl. XI. figs. 1-5. 
Daphne curvirostris, O. F. Muller, Zool. Dan. Prod. p. 200. No. 
2403. 
Daphnia curvirostris, O. ¥. Miller, Entomostraca, p. 93, pl. 13. 
f,1.& 2. 
Acanthocercus rigidus, Schodler, Archiv. fiir Naturgeschichte, 
1846, B.i. p. 301, pl. 11&12. Lievin, “ Die Branchiopoden 
der Danziger Gegend,” Neueste Schriften der Naturforschen- 
den Gesellschaft in Danzig, B. iv. p. 33, pl. 8. f. 1-5. Leydig, 
Naturgeschichte der Daphniden, p. 195. 
Acantholeberis curvirostris, Lilljeborg, De Crust. ex ord. Clad. 
Ostrac. et Copep. p. 52, pl. 4. f. 83-7, & pl. 23. f. 10, 11. 
The carapace is somewhat oblong in form, rather truncate 
below, and with the hind margin nearly straight, since the ma- 
trix is but little protuberant.in the gravid female. The head 
does not lean forward, as is usually the case among the Daph- 
niide, but is remarkably upright. To the upper point of the 
beak the anterior antenne (Pl. I. fig. 2) are attached, and from 
it they are projected at nearly a right angle. These organs are 
very large, and strap-shaped; they are slightly serrate on the 
upper margin, and gradually widen towards the extremity, which 
is furnished with six or eight cylindrical tentaculiform filaments: 
The supplemental eye-spot is situated close behind their bases, 
and is very small. 
