Fresh-water Entomostraca of South America. 29 



close to the tip of the rostrum. Antennulæ narrow linear 

 in form, with- about 7 transverse rows of spikes, sensory 

 bristle close to the base, apical papillæ not very elongated. 

 Antennæ scarcely more than half the length of the body, 

 rami subequal in length, proximal seta of lower ramus but 

 slightly longer than the others, and scarcely different in struc- 

 ture. Caudal part exceedingly large and lamellarly expanded 

 behind, slightly tapering distally, dorsal edge forming above 

 the anal orifice 2 even convexities, the lower one about twice 

 as long as the upper, and both defined by a well-marked 

 incision; anal denticles disposed on each side in 3 separate 

 sets, 6 or 7 occurring in front of the anal orifice, 4 or 5 at 

 the side of the same, somewhat remote from the edge, and 

 a single rather elongate denticle immediately behind this 

 orifice, at some distance from the others; caudal claws each 

 with a small basal spinule, their concave edge finely denti- 

 culate; caudal setæ attaining about half the length of the 

 body, and having the distal joint coarsely ciliated. Ephip- 

 pium rounded quadrangular in shape, egg-chambers reni- 

 form, turning the concave side towards each other. Male 

 much smaller than female, with the dorsal margin of the 

 carapace straight. Antennulæ with an additional spiniform 

 bristle at the base. First pair of legs terminating in a very 

 small and but slightly curved claw. Caudal part not trans- 

 formed. Colour of female more or less bright reddish brown. 

 Length of adult female reaching 0.85 mm., that of male 

 0.52 mm. 



Remarks. — About the specific identity of the above- 

 characterized form with that described by Mr. Eichard, there 

 can be no doubt. In the accompanying plate I give care- 

 fully drawn figures, habitus and details, of this interesting 

 form, to show more clearly its relation to other Macrothri- 



