INSECTS ERRONEOUSLY REFERRED TO BUTTERFLIES. 93 



and with their branches support nearly the entire wing; the subcostal nervure 

 curves downward and the median upward so as to meet, or nearly to meet, not 

 far from the middle of the wing, and to enclose between them a large space 

 called the discoidal cell; the branches of the median nervure are all thrown oft 1 

 from its lower edge before union with the subcostal; the principal branches of 

 the subcostal nervure are, on their side, thrown oft* from its upper edge; but, 

 as the nervure curves downward at the extremity of the cell, another set is 

 thrown off (at least in the fore wings) from the lower edge; and it is these 

 veins, rather than the subcostal nervure proper, which unite with the median to 

 close the cell. 1 None of the median, nor any of the inferior subcostal nervules 

 are ever branched; but at the apex of the wing, where the play of neuration is 

 usually the greatest, the last superior subcostal nervule is occasionally forked 

 in the front wing. This is the only forked branchlet in either of the wings. 



The last figure of P. oolitica given by Mr. Butler agrees in all its essential 

 features with his first illustration. They both represent a front wing with four 

 principal nervures, costal, subcostal, median and submedian; the costal nervure is 

 swollen at the base and extends, unbranched, to the tip of the wing; the median 

 nervnre is three-branched, the three forks simple, equidistant, emitted from the api- 

 cal half of the vein, which at its extremity is united by a cross vein to a branch of 

 the' subcostal, closing the cell; the submedian nervure is simple and divides the 

 space between the median vein and the margin of the wing. So far all is in ac- 

 cordance with the lepidopterous type; but when we examine the subcostal vein, 

 which occupies nearly half the wing, the resemblance ceases altogether. This vein 

 is represented as bearing no superior branches, but as sending out from its inferior 

 surface three distinct veinlets, the first and second of which again emit a tributary 

 from their inferior surfaces. This is a structural anomaly which finds no counter- 

 part whatsoever in any family of butterflies. So that should we accept Mr. Butler's 

 own sketch of the fossil as correct, it would be impossible to consider the wing- 

 that of a butterfly. 



1 These veins have been given a distinct name (discoidal) by belonging to the wings ol' these insects. I have therefore pre- 



the English Entomologists, as if they had an independent origin, ferred to speak of them as the inferior subcostal nervules, in 



and hail nothing to do with the subcostal nervure; but by the use contradistinction to tlie superior branches of the same vein, 

 of tliis name, we wholly lose sight of the simple plan of ueuration 



MEMOIRS A. A. A. S. 14 



