NO. 1687. THE THORAX OF INSECTS— SNODGRASS. 589 



V, line oil dorsal surface of notum formed by venti'al V-shaped ridge, in some 

 Ortboptera (3S, 50), Coleoptera (131. 133, 137, 138), Neuroptera (143), 

 Lepidoptera (149, 150, 151, 156), Diptera (175, ISO). 

 w, transverse ridge or ridges on under surface of metanotuui in Coleoptera 

 or its line on tbe dorsal surface, dividing tlie scutum into two regions 

 (132-138, 140). 

 a?, ?/, 2;, anterior, middle, and i)<)sterior transverse external grooves and corre- 

 sponding internal ridges on pronotum of M('hiiioi)lus (51, 52). The 

 middle ridge (NK) takes place of pleural ridge. 



NiiiiihcriDff. 



J, 2, 3, Ii, first axillary (lAx), second axillary {2 Ax), third axillary {SA-e), 



and fourth axillary {Ji Ax) of wing base. 

 Roman numerals /-A' designate first to tenth abdominal segments, combined 



with letters T and S indicate terga and sterna of indvidual segments. 

 Figures 1, 2, and 3 placed behind and below an abbreviation refer it to the 



prothorax, mesothorax, or metathorax, respectively. 

 Figures J, 2, 3, etc., placed before an abbreviation signify first, second, third, 



etc. 



Plate 40. 



Fig. 1. llexngenia hUincatn, mesothorax nad base of wing, lateral. 



2. Hexagcnia hilincata, metathorax and base of wing, lateral. 



3. Hexagcnia bilineata, metatergum. 



4. Hexagenia hilincata, mesotergum and base of right wing. 



Plate 41. 



Fig. 5. LibeUula auripennis, adult, prothorax and microthorax, lateral. 



6. Libclliila auripennis, adult, plates of microthorax (nii), prosternum 



(8) and presternum {Ps). 



7. Pachydiplax longipcnnis, adult, prothorax, lateral. 



8. Lestes uncatus, nymph, microthorax and prothorax, lateral. 



9. Lestes wncatus, adult, microthorax and prothorax, lateral. 



10. Pachydiplax longipcnnis, adult, prosternum. 



11. Gomphus hrevis, adult, prosternum. 



12. Gomphus plagiatus, nymph, microthorax and prothorax, lateral. 



13. Gomphus hrevis, adult, prothorax, lateral. 



Plate 42. 



Fig. 14. Gomphus plagiatus, large nymph, meso- and metathorax, dorsal. 



15. Pachydiplax longipcnnis, small nymph, meso- and metanotum and 



bases of wings. 



16. Lihcllula pulchclla. nymph, meso- and metathorax, lateral. 



17. Pachydiplax longipcnnis, adult, meso- and metatergum and bases of 



right wings. 



18. Lihcllula auripennis, adult, meso- and metapleurum, external. 



19. Lihcllula auripennis, adult, metapleurum, internal. 



Plate 43. 



Fig. 20. Mccistocephalus sp., lateral view of a segment. 



21. Scolopocryptops sp.. fifteenth segment, lateral. 



22. Lithohius sp., a large segment, lateral. 



