340 A. H. Swinton — On Fossil Ortkoptera. 



This peculiarity, while it increases the transverse rigidity of the 

 pin'on, and seems to contract the marginal and internomediate fields, 

 also approximates the externomediate vein (3) to the principal limb 

 of the scapular (2), with which it coincides a little before the elbow. 



If we now turn to the Coalbrook-dale elytron, Plate XIV. 

 Fig. 3, we see this characteristic well marked, but in conjunction 

 with other elements, which deserve prominence from the indica- 

 tions they afford us of a slight aberration from the minor characters 

 in a wing of the cricket or Gryllacris type, this is obviously in 

 accordance with the increase of wing area, which here, it will be 

 observed, is twice as great as that of any recent species with which 

 we are acquainted. These modifications are briefly comprised in 

 the greater branching of the large longitudinal veins, and occasional 

 dividing of the transverse veinlets that brace them together, with the 

 less parallel disposition of the former. It is to be regretted that the 

 imperfect preservation of the Eocene insects forbids the institution 

 of accurate comparisons on these points, which certainly indicate a 

 greater expanse or decrease in toughness or elasticity in the wing 

 membrane ; and the more so as this wing seems to constitute a type 

 to which the fragments of the G. Uthanthraca, Heer, from the Saar- 

 briick Coal-fields, may be referable. 



File. — As a rule the file characterizes the male of the crickets and. 

 leaf-crickets, and although I cannot succeed in finding a species of 

 Gryllacris with an efi"ective file, it may nevertheless sometimes be 

 found beneath the base of the elytron of these insects in a mem- 

 branous form, as seen in Plate XIV. Fig. 1. Little more is to be 

 gained from an examination of the remains of G. TJngeri, which 

 only presents a circular vein of questionable import at the base of 

 the under side of the right elytron, marked by a few doubtful 

 indentations. 



In the Coalbrook-dale elytron the file is well marked, and judging 

 from the fact of its traversing the internomediate field of the elytron, 

 its form, the character presented in its lower extremity, where the 

 teeth are largest, it exhibits to us the nearest resemblance to the file 

 or lima of the male house-cricket, as figured by Newport or Landois. 

 (I have by me drawings of the file of the male European house and 

 field-crickets, and hand specimens of those of the males of various 

 leaf-crickets.) The house -cricket, as is well known, "sings" by 

 partially opening and shutting its raised elytra, during which the 

 file on the under side of the upper moves its teeth somewhat 

 diagonally over a vein at the upper surface of the opposite elytron 

 or wing-cover placed beneath, as Goureau has long ago informed us 

 in his able and interesting paper contained in the Annales de la 

 Soc. Entomol. de France. The mechanism of its file, as shown at 

 Plate XIV. Fig. 4, is from a drawing by Newport, and the micro- 

 scopic structure has recently been thus described by Landois : — 



" Each wing-cover in the cricket has a shrill vein for vibration, 

 analogous in form and position to that of the field-cricket. On its 

 under surface are numerous bridges, about 200 in niunber, projecting 

 from and placed crossways on the vein. In the cricket the bridges 



