6 SCUDDER ON THE DEVONIAN 



may be other shorter iBtercalaries ; the only exception to this general statement is the 

 case of Polymitarcys already cited, where after division at the base the ujiper fork must 

 be looked upon as breaking up at once into three rays, while the lower severed from its 

 connections breaks up similarly into a couple of forked rays ; the amount of abnormal 

 divergence in this case may be better seen, by stating that it is the only genus of Ephem- 

 eridaj in which this area is carried around the lower outer angle of the wing ; in all others 

 it stops short of, usually far short of this angle ; here it reaches around it half way along 

 the anal margin. The genus agrees, however, with all the others in that all the branch- 

 ing occurs in the basal half of the area. In Oligoneuria and Lachlania the branch is 

 simple and undivided, unless the apparent branch in the latter should be looked upon as 

 such, and not as a cross nervure, like the more directly transverse veins above it. 



The area of the internomedian vein is never great, although always more extensive than 

 that of any other vein but the externomedian, and it always includes the lower outer 

 angle of the wing, excepting as above specified in Polymitarcys, and excepting also in 

 the full-angled Tricorythus, where the anal area disputes its sway. Its construction is gen- 

 ei\illy similar to that of the lower branch of the extermomedian vein, although from the 

 form of the area covered Ijy it, its absolute appearance is very different ; moreover, one 

 rarely finds in it any intercalary nervures, excepting such as sometimes line the 

 extreme border, the smaller nervures almost always originating from the main stems ; 

 the exceptions are found in Leptophlebia, Cloeon, and Baetis. The vein almost invariably 

 forks at its extreme base, and from the upper of these branches sends either, rarely, a 

 single shoot, or, much more frequently, a half a dozen, occasionally a dozen simple or forked 

 shoots to the margin. In the interesting fossil described in the note at the end of this 

 section these shoots appear to originate from the lower branch, the upper remaining 

 simple, just as rarely occurs in living forms as e. <j., in some species of Leptophlebia. 



The anal vein invariably plays an insignificant part, and is apparently sometimes want- 

 ing. Its area seldom reaches even half way along the anal margin, but in Tricorythus it 

 extends even around the lower outer angle, fairly upon the outer margin. Here it is 

 composed of a single vein with three or four short but widely divergent branches ; usually 

 it is forked at the base, and occasionally one or the other of these forks imitates the rayed 

 branch of the internomedian by sending a number of parallel branches, often closely 

 crowded, to the margin. 



This account of the neuration of the Ephemeridae is based upon miich more extended 

 material, and a longer study than that formerly given by me in my first quarto paper on 

 fossil neuroptera, and corrects it in several important particulai's, especially in the account 

 of the internomedian vein, which was eroneously stated to be simple ^ and in the fuller 

 statement of the divisions of the externomedian vein. 



Note, on a Jurassic May-fly. 



Hexagenites Weycnherc/lm, gen. et sp. nov.: — A fragment of a wing only is preserved, in 

 which the entire costal area and base are wanting. 1'he neuration of the parts that remain 



I This statement wjis evidently tlie result of some over- same memoir it was remarked that the internomeilian vein 

 sight, siuee in the digest given on a subsequent page of the was " similar in tharaeter to the vena externoviedia." 



