NO. 1687. 77/ W THORAX OF INSIECTfi—f^XODGRASS. 553 



II. KPIIKXIKKIDA. 



ASpt'cics stiidU'd. — Ili'.rcKjehta hUhwatd (1, 2, )\, A), 



C/uu'dctci'isflcx. — Shows little similarity to otluM- orders of insects, 

 except to Odonata, which are suggested by structure of Aving articu- 

 lation. Xotuni and ])seudon()tuni ])resent in niesotergnni and nieta- 

 terguni. Lateral parts of niesonotum (4) complicated b}' irregular 

 confusion of elevations and depressions. Axillary c:)rds (.1,/' C) 

 arising from middle of jiosterioi* edge of notum, jiseudonotum hidden 

 from above. On mesopieurum (1) wing process (IIV) and pleural 

 suture {PS) present, but episternum and epimerum are regions not 

 definitely defined as plates. Epimeral region continuous wnth pseudo- 

 notum {PX). Wing Acins flexible at base, merging into edges of 

 tergum. Only one axillary sclerite developed (.^, lAx). Meta- 

 tergum smaller than the preceding (3), both notum and pseudono- 

 tum present. Metapleurmn Avith distinct Aving process {WF), but 

 Avithout definitely formed ])leurites or pleural suture. 



HI. OnONTA. 



SpeHcfi Hfvdied. — J.'ilxlhila foir'/pciinifi (5, G, 18, 10), L. f^ilcheVa 

 (IG), Pachydlplax longipenivis (T, 10, 15, IT), Libellulida}; Lestes 

 uncatus (8, 0), Enellacjma dnrurn^ xVgrionidje; Gomphus brevis (11, 

 13), G. plagiatus (12, 14), .Eschnida\ 



Characteristics. — 1. Microthorax represented in both nymphs and 

 adults by a number of plates on sides of the neck (5, G, 8, 9, 12, mi^ 

 1 mi., 2 mi., 3 mi^ Ji mi) closely associated Avith side of the prothorax 

 and forming a long arm on each side of neck reaching forAvard into 

 concavity of the back of head. 



2. Pronotum topographically divided inlo tliree distinct transverse 

 lobes (5, 7, 8. 9, 12, 13, .V), the third often witli a descending ])ostepi- 

 meral strip (5, T, 12, a). 



3. Prothoracic pleurum shoAvs an evolution from such simple forms 

 as shoAvn by nymph of Lestes unoatiis (8) and adult of Pachydiplax 

 hnigipennis (T) to forms such as Gomphus pagiatiis (12) and Gom- 

 phus hreris (13) Avhere epimerum (Fpm) forms principal plate on 

 side, episternum being divided into a small upper piece (eps) fusing 

 Avith epimerum (12), and into a larger ventral plate (Eps) fused 

 Avith lateral plate of presternum (Ps). 



4. Presternum (Ps) of the prothorax A^aries from a transA^erse plate 

 Avith expanded lateral part (11), to a condition where it consists of 

 two j^lates ind(>pendent of the sternum and lying at sides of the latter 

 (5, G, T, 0, 10). These plates in some forms, as shown under 3, 

 completely fuse Avith loAver subdiAnsion of episternum (11, 12, 13). 



5. Prosternum connected Avith the mesosternum b}^ tAvo slender 

 rods (G, 7, 10, 11, is, />). 



