Fresh-water Entornostraca of South America. 33 



11. Macrothrix elegans, n. sp. 



(PI. VI, figs. 1-9). 

 Specific Characters. — Female. Carapace some- 

 what compressed, seen laterally, oval in form, dorsal margin 

 evenly arched, and perfectly smooth, ventral very slightly 

 and somewhat irregularly curved, posterior extremity ter- 

 minating in an obtuse point placed somewhat below the axis 

 of the body. Head of moderate size, and not defined above 

 from the carapace by any distinct depression, though having 

 at this place a well-marked cervical organ; dorsal margin 

 gently curved and slightly bulging in the ocular region, ro- 

 stral projection very short; ventral face with about 5 trans- 

 verse ridges, giving the lower edge a serrated appearance. 

 Surface of shell sculptured with very distinct obliquely trans- 

 verse and somewhat curved striæ, partly anastomosing with 

 each other. Valvular part of carapace, as usual, rather small, 

 not permitting the tail to be wholly covered; lower edges 

 rather apart, and fringed with a double row of spiniform 

 setæ. Eye comparatively large, with very distinct crystal- 

 line cones; ocellus small, and located close to the tip of 

 the rostrum. Antennulæ of moderate size, and scarcely 

 widening at all distally, anterior face with 4 or 5 transverse 

 rows of small spikes, posterior with a rather strong spiniform 

 process near the tip, accompanied by a few slender hairs, 

 the tip itself denticulate, and carrying the usual bundle of 

 apical papillæ. Antennæ rather powerful, and of the usual 

 structure. Epipodite of the 1st pair of legs unusually large, 

 sigmoid in form, and extending in front, so as to reach be- 

 yond the anterior edge of the leg; that of last pair likewise 

 greatly developed, falciform. Caudal part comparatively 

 more elongated than in most other species, its basal por- 



3 — Archiv for Math, og Naturv. B. XXIH. Nr. 3. 

 Trykt den 11. Marts 1901. 



