Fresh-water Entomostraca of South America. 



dorsal margin but very slightly arched, ventral almost 

 straight, posterior extremity very obliquely truncated, upper 

 corner rather slight, lower considerably projecting and blunted 

 at the tip. Valves comparatively small, scarcely obtecting 

 the oral parts in front, free edges densely setiferous, some 

 of the setæ, issuing from the posterior corners, long and 

 divergent. Shell-gland angularly curved, without any posterior 

 ramus. Head very thick, pyramidal in form, seen laterally 

 less broad than in the 2 other species, with the end nar- 

 rowly rounded; ventral margin almost straight and obliquely 

 descending, dorsal slightly concaved behind. Fornices of 

 head distinct, though rather small, encircling above the 

 bases of the antennæ. Eye large, with numerous crystalline 

 cones, and as in the 2 other species, located nearer the 

 dorsal than the ventral face. Ocellus very small and at a 

 considerable distance from the eye. Antennulæ with the 

 flagellum not recurved, and but slightly exceeding the basal 

 part in length. Antennæ exceedingly powerful, upper ramus 

 with a greater number of natatory setæ than in any of the 

 other species, amounting to 21 in all, 12 of which are at- 

 tached to the distal joint, proximal joint rather broad, show- 

 ing a slight approach to the formation of a lateral expan- 

 sion as in Latona; lower ramus normal. Caudal part scarcely 

 at all deflexed, conically tapered, dorsal edge divided at the 

 base into 4 large serrations, and having another smaller 

 median projection near the end; anal denticles rather slight, 

 about 9 on each side; caudal claws with 3 slender curved 

 secondary spines at the base, their outer part finely denti- 

 culate and terminating in a very sharp point; caudal setæ 

 about twice the length of the caudal part, and rather strong. 

 Body highly pellucid, and almost colourless. Length of oviger- 

 ous female about 2 mm. 



