409] COLORS OF TIGER BEETLES—SHELFORD 15 



The elytral tracheation of the Cieindela has been observed by the 

 writei" in about one hundred species. The elytra of the newly emerged 

 ^magoes of ten North American species have been studied in some detail. 

 Nearly all the common North American species and about fifty exotic 

 species have been studied in less detail by mounting dried elytra in hot 

 Canada balsam containing little or none of the usual solvents. The 

 main tracheal trunks and some of the branches remain clearly visible 

 in such mounts for several hours. 



In terms of the system of classification proposed by Comstoek and 

 Needham, the usual tracheae present (Figs. 18 and 21, PI. II) are 

 the costa {Co) which branches near its distal end, and subcosta (S) 

 which lies close to the costa on the outer edge of elytron ; the radius {R) 

 and media (.1/) which lie in the medium portion of the elytron; the 

 cubitus (C») which lies along the suture, and {A) the anal rudiment 

 which lies next to the scutellum. 



The six tninks common in insects are represented in but two genera 

 (Aniblychila and JIantichora), which have rudimentary wings and 

 specialized elytra fastened together in the adult (Shelfoi'd, 1915). 

 These trachea are demonstrated in the adult dried elytra without any 

 difficulty. In Omus, which is closely related to Amblychila, the radius 

 and media have disappeared except for rudiments. The cubitus is the 

 principal trachea. With the exception of Omus and Amblychila it is 

 the anal that has degenerated farthest. Collyris was never veiy satis- 

 factory for study, but it appears that the cubitus is reduced and the 

 anal wanting. In Platychila pallida (Shelford, 1911: Fig. 7) the com- 

 monest type of tracheation of the family and probably among the most 

 generalized, so far as the first four trachea, are concerned, is shown. The 

 anal is much reduced. 



The munber of small branches and cross connections is large and 

 too variable to be correlated with other specific characters or with color- 

 pattern characters. Figures already published (Shelford, 1913: Figs. 10 

 to 19) illustrate this fact. The two elytra of an individual show a mark- 

 ed difference. It is evident then that only the main trunks are at all 

 constant. The costal branch at the center the posterior third of the 

 elytron at the beginning of the curve is very characteristic of Cieindela 

 but bears an important relation to color pattern only in some cases. 



Figures 2 to 33, plates I to III are selected to show the relation of 

 unpigmented ai-eas to the main traclieal trunks. Figure 2 shows four 

 cross bands which are cut across by the tracheae. Figures 3 and 4 show 

 the same type of pattern but with the cross bands narrower, the middle 

 one broken in the region of the trachea toward the right and with a sug- 

 gestion of two or three stripes. Figure 5 shows a similar condition but 



