BY ft. J. TILLYARt). 207 



the fossil should represent a portion of a large Wing of about the 

 same size as that of M. illidgei, viz., about 27 mm. long). All 

 the main veins and branches beautifully preserved, very strongly 

 formed; the cross-veins, which are only present between Sc and 

 R,, and between R, and Rs, are weak and difficult to make out, 

 but can be clearly seen in oblique evening sunlight. Sc, R,, Rs, 

 and Cu, are exceptionally strong veins, as also in M. illidgei. 

 The direction of Cu,, which makes an angle of as much as 50° 

 with Rs, is quite exceptional, but is about the same as in the 

 forewing of M . illidgei; likewise the weak formation of Cu 2 , and 

 its position parallel and very close up to Cuj, is similar in both. 

 No less than ten branches of Rs are present in the preserved 

 portion of the wing; so that the total number of branches must 

 have been very large, as also in M. illidgei. The formation of 

 M is peculiar. Owing to the strength and thickness of Cu 1? 

 which stands on a high ridge, it is not easy to make out the 

 exact formation of the much weaker concave vein M near its 

 base. Rut, viewed with a good light in the right direction, there 

 can be seen a weak posterior branch of M arising from the main 

 stem quite close to the base, and running between and parallel 

 to M and Cu,, until it meets with an oblique cross- vein descend- 

 ing from M just before the first clear dichotomy; it then curves 

 in to join Cu, just below the dichotomy of M. Reing in doubt 

 as to the interpretation of this peculiar formation, I examined 

 the forewing of M. illidgei, and there found, in the same position, 

 a distinct but weak branch of M arising in the same manner, 

 and ending on a cross-vein descending from the first evident 

 dichotomy of M, as shown in Text- fig. 28, a. As this character 

 appears to be of some importance, I also examined the forewing 

 of Pagchopsis elegans (Guer.), and was surprised to find a closely 

 similar formation there. I think that there can be little doubt 

 that this vein, which I unfortunately overlooked in my previous 

 studies of the Psychopside;, is really the posterior branch from 

 the first dichotomy of M, and should therefore be called M B . It 

 must evidently be the homologue of the vein called the posterior 

 arculus by Comstock in the Trichoptera and Lepidoptera, and 

 also visible in the Mecopteron Stereochorista described on p. 196 



