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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVU. 



excavate hind marj>-in. Antenna longer than the head, six, possibly 

 seven, jointed, the last suture being indistinct, the ratio of the seg-, 

 ments from the base outward being as 1 : l.-i : 1.8 : 1.3 : 1.1 : 1 : .3 ? 

 The labium (fig. 9) is of moderate size. The mentum is regularly 

 widened to the base of the lateral lobes. The median lobe is moder- 

 atel}^ prominent, smooth on the edge and with straight sides. Mental 

 setse four (in one case on one side three) each side. Lateral lobe with 

 six setfe, a stout movable hook, three distinct 

 teeth on the end above the end hook, and the 

 outer angle angulate with unusual sharpness, its 

 margins scarcely edenticulate. 



The legs are rather short. The wing cases reach 

 posteriorly as far as the middle of the fourth 

 abdominal segment. 

 The abdomen is cylindric, with segments of nearly equal length, 

 slightly diminishing in diameter toward the end, the tenth segment 

 somewhat emarginate on its superior apical margin. Gills (fig. 10) 

 oblong-oval, widest just beyond the middle, broadly rounded at the 

 ends, and with somewhat darker pigmentation along the axis. 



Fig. 10.— Middle gill 

 lamella of nymph of 

 Hesperagkiox hetero- 



DOXUM. 



LEPTOBASIS sp.? 



Four nymphs, not fully grown, collected by ]Mr. August Busch at 

 Catana, Porto Rico, in January, 1S99. 



Length, 13 mm.; gills, 1 mm. additional; width of head. 3 nmi. ; of 

 abdomen, 2 mm. 



Slender, pale, short-legged njmiphs, with broad, depressed head, 

 large, laterally prominent eves, behind which the sides slope abruptly 

 to the obtuselj^ prominent hind angles, be- 

 tween which on the rear of the head is a 

 deep and well-rounded excavation. Anten- 

 na longer than the head; ratio of segments 

 1 : 1.2 : 1.5 : 1.1 : .6 : .4. Labium moderate, 

 its hinge reaching backward as far as the 

 mesothorax, its median lobe very prominent, with serrulate margins, 

 the serrulations directed laterally, and, therefore, in opposite directions 

 on the two concave sides. One mental seta only each side. Lateral 

 setae, 3. End of the lateral lobe above the end hook with a series of 

 1^5 minute recurved denticles, diminishing in size to the outer angle. 



Legs short and rather slender. Wings reaching as far back as the 

 apex of the fourth abdominal segment. 



Abdomen cj'lindric, the segments of about equal length, or the two 

 hindmost slightly shorter than the others and narrower. Gills (fig. 11) 

 oblong, obtuse at apex, with a broad longitudinal difluse pigmented 

 axial tract, and pale margins. Each gill is divided transversely across 



Fig. U.— Middle gill lamella of 

 nymph of leptobasis sp.? from 

 Porto Rico. 



