48 S. II. SCUDDER OX PALAEOZOIC COCKROACHES. 



Lithomylacris nov. gen. (Xtftos, /wAaxpfe). 



The mediastinal vein of the upper wings consists of about five principal shoots, only 

 two or three of which fork and these generally close to the base, all of them straight or 

 gently curved, and the outermost extending to variable distances along the costal margin, 

 but generally beyond the middle of the wing; the point toward which these branches 

 converge is considerably nearer the inner than the costal margin of the wings; this with the 

 great length of the outermost shoot gives the mediastinal area an unusual extent for Myla- 

 cridae. The scapular vein is considerably curved before branching, but beyond its first 

 branch is almost exactly straight, even the outer portion scarcely curving, and runs down 

 the middle line of the wing to the tip, so that the mediastinal and scapular areas together 

 occupy full} 7 half of the wing ; it emits four or five branches, more or less closely approxi- 

 mated, according as one or two of them fork or not, ami all run subparallel to, but rather 

 less obliquely than, the outer branches of the mediastinal vein. The externomedian area 

 is very narrow and of small extent, occupying the lower half of the narrow tip of the 

 wing, the vein first branching at or beyond the tip of the wing, and then but once or 

 twice, either superiorly or interiorly, the first branch sometimes forking. The interno- 

 median and anal veins together divide nearly ecpially between them the inner margin of 

 the wing, the anal furrow being rather conspicuous and gently arched, and, from the 

 narrowness of the wing and the inferior position of the common point of origin for all the 

 principal veins, unusually longitudinal, most of the species differing in this respect some- 

 what conspicuously from those of Mylacris; the internomedian vein has only two or 

 three branches, which are very longitudinal and very long, and yet fork comparatively 

 little, rarely doubly; the vein may emit its first branch somewhat before, opposite to, or 

 considerably beyond the origin of the first branch of the scapular vein. The branches 

 of the anal vein are known only in one species, where they are parallel, rarely fork, and 

 are slightly more longitudinal than the branches of the internomedian vein. 



The wings are remarkable for their elongate form and nearly parallel sides ; the greatest 

 breadth is at about the middle and they are generally three times as long as broad, being 

 exceptionally slender for Mylacridae. 



Upper wings are all the remains known of this genus, which differs from Mylacris in the 

 more attenuated and equal shape, the slight obliquity and gentle curve of the anal furrow, 

 the slight importance of the externomedian area, and also by the unusual sulfation of the 

 interspaces between all the veins ; from Necymylacris it is readily separated by the very 

 wide extent of the combined mediastinal and scapular areas. The species are all of rather 

 small size and are found only in America. 



Lithomylacris angustum nov. sp. Rl. 5, figs. 2, 3. 



The fore wing is long and very slender, the inner margin straight, the costal margin 

 very gently and regularly convex ; the wing narrows from the middle, at first very slightly, 

 in the apical fifth more rapidly; the tip is broken in part, but was evidently well rounded 

 and, from a less rapid narrowing of the wing, probably not so slender as in the preceding 

 species. The veins take their rise from a point considerably below the middle of the wing, 

 the lower ones scarcely curving upward in passing outward, the upper ones curving very 

 gently and broadly next the base. % The mediastinal area is fully half the width of the 



