ivith Descriptions of New Forms. 125 



rapidly from about the- seventh to the tenth segment. The 

 thorax is unusually large in proportion to the abdomen, 

 being approximately twice as broad and twice as long as 

 the abdomen. A later stage is represented by a specimen 

 14 mm long, and presents much the same proportions. The 

 wing pads have become larger and the front pair now some- 

 what overlap the second pair. The specimen shown in Figure 

 3 has reached a length of 2 cm , exclusive of the head and cerci. 

 The head as seen on this and other specimens is large ; the 

 eyes are here preserved as elongate ovate impressions. The 

 largest specimens, which are presumably approaching maturity, 

 are 3 cm in length. The pronotum in these later stages becomes 

 slightly rounded at the lateral angles, the front wings are notice- 

 ably larger than the hind, and traces of the venation have 

 appeared. The adult, when identified, will probably be found 

 to have a broad pronotum rounded at the lateral corners, with 

 wings longer than the short abdomen, and resembling in a gen- 

 eral way the adults of M. elongata, which has, however, a pro- 

 portionally longer thorax and a more strongly arched boxlike 

 body. The most striking character of the species in its larval 

 stages is the short abdomen and the large, broad thorax.- The 

 antennae, cerci, sterna, and parts of the legs have been observed. 

 The nymphs, not having been identified with the adults, may 

 conveniently retain for the present the specific name already 

 assigned to them. The reference of the species to the genus 

 Mylacris is provisional, Mylacris being used, as explained 

 above, in a general sense for nymphs of the Mylacridce* 



Formation and Locality. — All the known specimens of this 

 species are from the Coal Measures at Mazon Creek, Illinois. 



Mylacris elongata. Text-figures 6-9; and Plate I, Figure 1. 

 Scudder, Bull. No. 124, U. S. Geol. Surv., p. 41, pi. i, fig. 6, 1895. 



The thorax of the nymph referred to this species is large, 

 the larger front wings overlapping the hind ones. The mould 

 of the dorsal surface, from which Figure 6 is made, shows the 

 ten segments of the abdomen. The first to the third terga are 

 reduced. The abdomen is broadest at the fifth segment, and 

 narrows to the tenth. The ninth and tenth terga of this 

 species appear to be closely united, the last being small. A 

 thickened line extends from the ninth across the tenth. The 



* Mr. A. L. Melander, in a foot-note accompanying his reference cited in 

 the synonymy above, suggests that the pronotum of this form agrees very 

 well with that of Promylacris rigida. From a direct comparison of the 

 types of the two species it seems probable that the pronotum of Promylacris 

 rigida, which in the type specimen is distorted, and from which, moreover, 

 the matrix has never been entirely removed, is proportionally less broad 

 than that of M. diplodiscus. 



