X. The Species of Mtlacris, a Carboniferous Genus of Cockroaches. 



By Samuel H. Scudder. 



Rend May 24, 1 82. 



M- 



.YLACRIS was first suggested by me as a name for a genus of paleozoic cockroaches in 

 1S68, but its full definition from other cockroaches was nit given until eleven years later 

 in my memoir on paleozoic cockroaches, when five species, two of them new, were fully 

 characterized and figured. It is the principal genus of the tribe Mylacridae, the distinct- 

 ively American group of ancient cockroaches, and by the facts known three years ago 

 appeared to be confined to the lower or middle coal measures. Through the indefatiga- 

 ble efforts of Mr. R. D. Lacoe of Pittston, Penn., whose explorations of the coal measures 

 of the United States have yielded better results for fossil insects than those of any other 

 person, I am enabled in this paper to double the number of species, besides giving addi 

 tional information concerning an imperfectly known species, nearly all the additional 

 forms coining from the coal measures of Pennsylvania ; not all, however, as before, 

 from the lower ami middle series, hut also from the upper coal measures, showing that 

 Mylacris has the same range as Litho.nylacris. The species of the genus may be dis- 

 tinguished by the following table. 



Key to the Species of Mylacris. 



Extcrnomedian veins superior or apical. 2 



Exteniomedian veins inferior or apical. 7 



Externomedian veins distinctly superior. 3 

 Extcrnomedian veins rather apical than su- 

 perior. 5 

 Apex of wing falling in the middle line, 

 the costal and inner margins being about 

 equally arcuate. 1. J/, bretom nsis. 

 Apex of wing falling below the middle line, 

 the inner margin being much straighter 

 than the costal. 4 

 Costal margin curving inward on the basal 



third of the wing. 7. M. anthracophilum. 

 Costal margin bent abruptly inward at ex- 

 treme base of the wing with no previous 

 inward curve. 8. M. priscovolans. 



MEMOIR8 BOST SOC, NAT. HIST. \<>1.. III. 



1. 



1. 



2. 



2. 



3. 



3. 



4. 



4. 



5. Extcrnomedian area occupying the apex of 



the wing. 2. M. Heeri. 



5. Extcrnomedian area falling wholly below the 



middle line of the wing. 6 



G. Mediastinal veins comparatively few and 

 distant; scapular vein forked at brse. 



3. If. antiquum. 



6. Mediastinal veins numerous ; scapular 



branches all emited from a single main 

 branch. 4. 31. lucifugum. 



7. Costal much more curved than inner margin. 8 



7. Costal and inner margin similarly and sym- 



metrically curved. 9 



8. Costal margin very strongly curved in the 



mediastinal area, which scarcely reaches to 

 the middle of the wing. 6. M. carbonum. 

 so 



