I D T M I D E A. 709 



of the outer. Outer antennae rather stout, last joint shorter than 

 preceding, long ovate, pubescent. Third pair of feet twice longer 

 than the first. 



Plate 46, fig. 9 a, animal, enlarged ; b, inner antenna ; c, extremity 

 of outer; d, view of mouth, in position showing maxillipeds and part 

 of mandibles; e, mandible; /, first maxilla; g, second maxilla; h, 

 first pair of abdominal appendages; i, second pair; &, outer pair; I, 

 tarsus. 



Rio Negro, Northern Patagonia. Taken from the stomach of a 

 Silurus. 



Length, nine or ten lines. Colourless when obtained. Length of 

 body full six times its width. The head and first thoracic segment 

 together longer than broad; fourth, fifth, sixth thoracic segments 

 longest, the fourth nearly quadrate. Outer antennae shorter than 

 half the body; last four joints each oblong. Basal joint of inner 

 antennae stoutish, third shortest, obconical; the fourth as long as 

 second and third together. 



Legs compressed; last joint longest. Claw with a short spine 

 beneath the apex. The three anterior pairs were thrown forward, 

 and reached alike just beyond the front of the head ; the others were 

 spread laterally. Inner oval lamina of exterior abdominal plates 

 ciliated, much shorter than the other plate with which it is asso- 

 ciated. 



Genus EMCHSONIA, Dana. 



Antennce externce valcle longiores, geniculatce, §-articulatce, flagello nullo, 

 sed articulo obtuso confectce, subclavatce. Pedes subcequi, quarti tertii- 

 que non valde incequi. Oculi mediocres, remoti. 



Outer antennae much longer than inner, geniculate, six-jointed, ending 

 in an obtuse joint and no flagellum, subclavate. Feet subequal, 

 the third and fourth pairs but little different in size. Eyes of 

 moderate size, remote. 



