INSECTS OF NEW BRUNSWICK. 9 



modern EphemeridsB generally, there is no intercalary nervule between this lower 

 branch of the uppar externomedian stem and the first oiFihoot of the lower branch, but 

 this interspace is filled with simple and frequent cross veins. 



The lower externomedian stem is apparently formed on the same plan as the upper, a 

 feature which appears to have no counterpart among living Ephemeridae ; apparently it 

 is composed, like the upper, of two primary branches, which seem to part from each other 

 very nearly at the same considerable distance from the base, (about one-third the distance to 

 the margin), a feature uncommon but not unknown in living Ephemeridae ; but instead of 

 having a single independent intercalary or two between the forks, it has several offshoots 

 which depend from the upper branch, ju?t as the offshoots of the upper branch of the 

 upper stem do, while between them in the outer half of their course other intercalaries 

 arise, depending from angular cross veins — the whole united by frequent cross veins 

 (again as in the upper area), to form a mesh-work of irregular cells generally pentagonal, 

 although not often longitudinal ; there are thus included between these forks about six 

 rows of cells. The interspaces directly adjoining either side of the lower branch of the 

 upper externomedian stem are slightly wider than the interspaces between the nervules in 

 the area of the lower externomedian stem, possess no intercalaries, and are divided by 

 frequent cross veins. The lower branch of the lower externomedian stem also curves 

 downward at the tip, like the lower branch of the upper stem ; the area of the lower 

 externomedian stem repeats, therefore, and on only a little smaller scale, the structure of 

 the area of the upper stem, instead of exhibiting, as in recent forms, distinctive features. 



That portion of the fragment of the wing lying below what we have here considered 

 the lower simple branch of the lower externomedian stem, and which is shown in fig. 10 

 and not in fig. 9, is so fragmentary and so separated from its basal connections that it is 

 difficult to decide to what area of the wing it belongs; it consists of four rows of cells 

 separated by curving nervules a little more uniform in their course than the minor 

 nervules above, with slightly less frequent cross veins ; the cells being slightly larger and 

 more regular, frequently quadrangular and usually longitudinal ; this field belongs of course 

 either to the externomedian or the internomedian area. The general similarity of the 

 structure of the fields would lead one at first to suppose it to belong to the externomedian 

 area, in which case of course our description of the lower stem and its branches should be 

 modified to receive it. As, too, the form of the fragment would indicate that a very 

 considerable part of the region about the anal angle is lost, the reference of this field to 

 the internomedian area would give that area a very great and very unusual preponderance 

 in the wino-. But its reference to the externomedian area, which is certainly possible, 

 would involve quite as great an anomaly ; for in that case the lower externomedian stem 

 must be supposed to consist of two branches, the lower lying beyond the present 

 fragment and probably simple, the upper forked and reproducing on a smaller scale the 

 whole of the upper externomedian stem, including the minor offshoots depending from the 

 uppermost branch of each. In this case the area of the lower stem would exceed that of 

 the upper, which occurs in very rare instances in modern Ephemeridae and then only by 

 crowdino- out of room the lower areas, which the probable wide expanse of this wing would 

 not allow unless this lower area is of an exceedingly disproportionate size. The 

 translation of the facts which I have offered in my description, on the other hand, while it 



