INSECTS OF NEW BRUNSWICK. 5 



the vein, and this number we find in Oligoneuria and, perhaps, in Lachlania. The 



portion of the area of this vein covered by the upper branch and its forks is almost 



always greater, generally considerably greater, than that covered by the lower branch ; 



an exception to this will be found in Polymitarcys where the lower area is greater, 



owing to unusual breadth of wing combined with narrowness of the area covered by 



the intermedian vein, which has been crowded out of much of its natural ground by 



this lower branch. Some of the allies of Polymitarcys, especially Asthenopus and 



Pentagenia, also have this area of the lower branch larger than usual, although not 



larger than that of the upper branch, and some other genera not placed near it exhibit 



a similar propensity ; but as a general thing, the area covered by the lower is scarcely 



more than half as large as that covered by the upper branch, and not infrequently it is 



less than one third its extent. The upper branch usually forks close to the base, 



occasionally at the very base, and sometimes the upper of the forks is amalgamated 



at the base with the scapular vein, as in Asthenopus, Tricorythus and Chloeon, and 



to a certain extent in Coenis, so as to give it the appearance of originating from that 



vein, and of complete independence of the externomedian ; whether thus severed from its 



connections, or plainly arising from the externomedian root, this upper fork of the upper 



branch runs in proximity to the scapular vein, parallel or subparallel to it, and, excepting 



wtere the venation is occasionally simple (as in Oligoneuria, &c.), always emits from its 



lower surface in the central portion of the wing one, two, or three nervules ; the first 



and second of these nervules are usually pretty near together at base, but all generally 



reach the border at unequal distances apart, the inequality being made good by 



intercalary longitudinal nervules ; these intercalary nervules often curve at their inner 



extremities toward or to one or another of the adjoining nervules, assuming then the 



appearance of regular branches, while the nervules proper are themselves oftener 



detached from their base ; so that it is sometimes difficult to tell whether a given vein 



should be considered normal or intercalary. The lower fork of the upper branch is 



occasionally simple, as in the Tricorythus, but usually forks once at about the middle 



of its course, rarely near the base, and very frequently encloses an intercalary nervule 



between these branches, but no intercalary nervules (excepting such as often break 



up the extreme margin into an irregular meshwork of veins) ever intervene between the 



upper nerviile of this fork and the lower nervule of the upper fork, nor between its 



lower nervule and the upper nervule of the lower branch of the externomedian vein, 



excepting in the rare instances where this lower nervule is detached from its base, and 



takes on the form of an intercalary nervule. 



This lower branch, as has been said, is usually forked to a less extent than the upper 

 branch, but a conspicuous exception is found in Polymitarcys where the branch is made up 

 of a large number of sub-convergent simple rays, directed from the outer margin 

 toward various parts of the upper internomedian nervule, but generally lost before reaching 

 it. In general; however, its area is only about half that of the upper branch ; it usually 

 forks close to the base, and each or either of its branches may again subdivide once ; all other 

 nervules in the area are sure to be intercalary ; where it forks only once there is usually 

 a single intercalary nervure midway between the branches, which seems to belong to one 

 or the other of them and to represent its fork ; while between it and either branch there 



