179 



segment comparatively large, being fully as long as the 4 succeeding segments 

 combined, epimeral parts exhibiting in front of the middle a very conspicuous 

 sinus. Rostrum very prominent, lanceolate. Urosome almost as long as the 

 anterior division, and slightly attenuated behind, anal segment scarcely shorter 

 than the preceding segment. Caudal rarni short, quadrangular, broader than they 

 are long, apical setse only slightly thickened at the base. Eye well developed. 

 Anterior antennae rather slender, 8-articulate, 4th joint almost twice as long as 

 3rd, terminal part half the length of the proximal part. Posterior antennae with 

 the outer ramus about as long as the terminal joint of the inner, and distinctly 

 3-articulate, middle joint well defined and setiferous. 1st pair of legs compara- 

 tively slender, outer ramus considerably shorter than the 1st joint of the inner, 

 middle joint with a well-developed seta inside, last joint of about the same length, 

 and armed with 3 spines and 2 geniculated setse; inner ramus with the 1st joint 

 very slender, more than twice as long as the other 2 combined, last joint about 

 twice as long as the preceding one. Natatory legs with the inner ramus in the 

 2 anterior pairs scarcely shorter than the outer, last joint of outer ramus in these 

 pairs with only a single seta inside. Last pair of legs with the distal joint rather 

 large, broadly oval in form, and provided with 6 marginal setse, the 2 apical ones 

 very thin, hair-like; inner expansion of proximal joint narrow triangular, extend- 

 ing beyond the middle of the distal joint, and carrying 5 spiniform marginal setse 

 of nearly equal size. Ovisacs of moderate size. 



Male with the inner ramus of 2nd pair of legs transformed in the usual 

 manner. Last pair of legs much smaller than in female, with the distal joint of 

 far inferior size, and only provided with 5 setse ; inner expansion of proximal joint 

 conically produced, and carrying 2 subequal setse on the tip. 



Colour not yet ascertained. 



Length of adult female 0.80 mm. 



Remarks. This form, both in size and general appearance, bears a per- 

 plexing resemblance to A. longirostris Glaus. It may, however, be at once dis- 

 tinguished from this form, in its lateral aspect, by the shallower cephalic segment, 

 and still more by the very conspicuous sinus which the epimeral parts form in front 

 of the middle, a character which has given rise to the specific name here proposed. 

 Moreover the structure of the outer ramus of the posterior antennae, and that of 

 the legs, is somewhat different. Finally, the innermost but one of the caudal setse 

 does not exhibit any trace of the peculiar bulging at the base found in A. lon- 

 girostris. 



Occurrence. ^l^ species was also found last summer occasionally in the 

 same locality in which the 3 preceding new species occurred. 



