572 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 52. 



in that of anterior end; middle lobe convex, with 30-35 bristloliko 

 scales; each lateral lobe with a cresentic tip turned inward at right 

 angles; on the concave edge 3-4 large rounded teeth. Burrowing 

 hooks rudimentary on both first and second tibiae. Wing pads reach- 

 ing segment 4. Abdomen lanceolate, tapering regularly, subcircular 

 in cross section. A dorsal groove on segments 3-7. A minute mid- 

 dorsal spine on apex of segment 9. Lateral hooks on segments 6-9, 

 those on 9 reaching to base of 10. Segments 3-8 subequal; segment 

 9 one and a half times the length of 8; segment 10 three-fifths length 

 of 8. Appendages equal to 10. (See figures 314 and 318-320.) 



Length, 38 mm.; abdomen, 26; hind femur, 5.5. Width of head, 

 6 mm.; abdomen, 7. 



Described from 6 exuviae collected on the Humbolt River at 

 Golconda, Nevada, August 9, 1914. The river at this point flows 

 through an alkaline, salt-grass flat. As it meanders it undermines 

 tlie salt grass sod which caves into the edge of the stream in large 

 squares. It was on these sods that the exuviae were found. 



GOMPHUS SOBRINUS, nymph. 



A heavy thick-skimied exuvia usually thickly coated with mud 

 because of a dense coat of very short spiny hau"s, differing noticeably 

 in this regard from donneri exuviae, which have few hau-s and these 

 usually very clean. General shape intermediate, neither short nor 

 slender. Abdomen much less arched than in donneri. It is distin- 

 guished by the following characters: Mentum of labium slightly 

 longer than wide, its posterior edge three-fifths to two-thirds width 

 of anterior edge, its sides instead of being sinuate suddenly con- 

 tracted proximad, making a sharp angle or "step" on either side. 

 (A small percentage of the specimens is intermediate in this mental 

 character, the "step" of the side being more sinuous.) Middle lobe 

 of mentum convex and fringed with about thirty bristle-like 

 scales. Lateral lobes broad at base, tapering regularly to a cres- 

 centic tip, the inner margin of which bears 7-9 low rounded teeth, 

 followed by smaller ones toward the base of the lobe. Well devel- 

 oped burrowing hooks on both first and second tibiae. Wing pads 

 reaching middle of segment 4. Abdomen lanceolate, slightly con- 

 tracted at base of segment 9, only moderately arched, its ventral 

 surface much flatter than in donneri. No dorsal groove, but apex of 

 segments 2-7 with a low rounded middorsal tubercle. A minute 

 middorsal tooth, hardly discernible, as it is concealed in a tuft of 

 hairs on apex of segments 2-7, larger on segments 8 and 9. Lateral 

 hooks on segments 6-9, those on segment 9 one-third the length of 

 10. Segments 2-8 subequal in length. Segment 9 one and a half 

 times the length of 8; segment 10 two-thirds the length of 8. 

 Appendages equal to 10. (See figs. 317 and 326-328.) 



Length, 38 mm.; abdomen, 26; hind femur, 5.5. Width of head, 

 6 mm.; abdomen, 7. 



