126 FOSSIL 1XSKCTS OF TITK BRITISH COAL MKASFUES. 



form of the Arclrimylacridse. Re-examination of the type-specimen shows errors 

 in the earlier descriptions and figure, and I uo\v re-describe and re-figure the type, 

 placing it in the new genus established l>y I'ruvost. 



The wing is a stout structure, with a coriaceous surface which has enabled it to 

 be perfectly preserved. The costal margin is well rounded inwardly at the base, 

 and flattens over the middle of the wing. Assuming that it agreed with wings ot 

 a I'hylomylacrid type, the margin would gradually merge distally into a broadly 

 rounded apex. 



The subcostal vein is the weakest of the whole series, and passes obliquely 

 outwards, reaching the margin about the middle of the wing. It gives off five 

 undivided branches which are oblique in direction, and fail to reach the margin. 



The costal area is broad basallv, and ends in an acute angle against the margin. 

 It may be best described as pyriform. 



The radius is a powerful vein, giving origin, in the inner third of the wing, to 

 what seems to be a well-marked radial sector, and dividing into two equal branches 

 a little further out. The outer of the two distal branches divides by twice forking 

 into three twigs, which may have reached the middle of the outer margin. The 

 inner of the two branches forks once only. 



A wide area separates the radius from the subcosta over the greater part of its 

 length, the widest interval being at the point where the radius divides into two 

 main branches. The branch (? radial sector), of which but few divisions are 

 shown on the wing-fragment, diverges inwardly from the main stem of the radius 

 into the middle of the wing, giving off two branches, the first forking close to the 

 broken edge of the nodule. Krom its position the ultimate divisions must have 

 ended upon the outer half of the Aving-apex. and the distal part of the outer 



AV ing- margin. 



The various divisions of the radius are so divergent that thev enclose a con- 

 siderable portion of the whole wing, while they are equally well spaced out from 

 the subcosta in front, and the median behind. The bast' of the radius stands up 

 in relief, and owing to a little enfolding of the wing, overhangs the bases of the 

 median and cubitus, but does not unite with them. 



The median vein arises close to the radius, and like the latter, bends inwards 

 at the base in a strong curve, which is continued until the direction is obliquely 

 inward, when it becomes straightened. 



At the summit of the basal curve the median sends off a short oblique vein 

 inwards to the cubitus. This vein is a distinct commissure, and not an enlarged 

 Interstitial nerviire. The significance of this eonimissural vein is not yet fully 

 understood. I'ruvost has recorded a similar structure in species of the genus 

 Archimylacris (<>/>. //., p. L 51), and mentions that Scudder and llandbrsch have 

 also indicated iis occurrence in other forms. ll is not, however, present in 

 Archimylacris iruuilinirtli, IJolton, and . I. l/itxl<i/n, IJolton. 



