124: 



Sellards — Structure of Paleozoic Cockroaches, 



present the more primitive structure and are not known later 

 than the Coal Measures. 



Mylacris. 



Mem. Boston Soc. Nat. 



Scudder, Geol. Surv. Illinois, vol. iii, p. 568, 1868 

 Hist., vol. iii, pt. 1, p. 40, 1879. 



Mylacris diplodiscus. Text-figures 2-4 ; Plate I, Figure 3. 



Dipeltis diplodiscus Packard, Amer. Nat., vol. xix, p. 293, 1885 ; Mem. 

 Nat. Acad. Sci., vol. iii, p. 145, 1886, pi. v, figs. 2 and 2 a . Schuchert, Proc. 

 U. S. Nat. Mns., vol. xix, p. 672, 1897, pi. lviii, figs. 2-5. Bernard, Nat- 

 ural Science, vol. xi, p. 397, December, 1897. Gahan, ibid., vol. xii, p. 42, 

 January, 1898 ; Schuchert, ibid., p. 215, March, 1898. Scudder, in Zittel's 

 Text-Book of Paleontolog3 r , Eastman's Translation, p. 687, 1900. Melander, 

 Journal of Geology, vol. xi. p. 185, Feb. -March, 1903, pi. v, fig. 6 ; pi. vii, 

 fig. 6. 



Mylacris diplodiscus Sellards, this Journal, vol. xv, p. 309, April, 1903, 

 pi. vii, fig. 8. 



Figures 2-4. — Mylacris (Dipeltis) diplodiscus ; all figures twice natural 

 size. Figure 2, after Schuchert. Originals of Figures 2 and 4 in the National 

 Museum ; original of Figure 3 in the Yale University Museum. 



This species is of much interest historically, having been 

 the first nymph cockroach described from this country, although 

 not recognized as such at the time.* No less than seven speci- 

 mens of this species in different stages of development have 

 now been obtained. The smallest individual observed, from 

 the National Museum collection, figured by Schuchert {loc. cit.), 

 and copied here (Figure 2), is hardly more than one centimeter 

 in length. The pronotutn is rounded in front and pointed at 

 the lateral angles. The wing pads appear as lateral extensions 

 of the thoracic terga, the two pairs being very similar in size, 

 shape, and texture. The abdomen is small, short, and narrows 



* For a history of Dipeltis and a redescription of the type specimen, the 

 reader may consult the short paper by the writer referred to above. 



