S. H. SCITDDER ON PALAEOZOIC COCKROACHES. 41 



so that the area of this vein generally occupies half the breadth of the wing, and together 

 with the branches of the mediastinal vein, half of the whole area of the wing; it emits 

 four or five branches, some of which fork, occasionally twice, and all of which run parallel 

 or very nearly parallel to the outer branch of the mediastinal vein ; to gain the apex and 

 to keep this parallelism the terminal part of the scapular vein curves gently upward. The 

 externomedian vein seldom forks before the middle of the wing and rarely occupies much 

 space, generally branching but three times at the most, although one or more of these 

 branches may have secondary forks ; generally these branches are so straight that it is 

 difficult to say whether they are superior or inferior to the main vein, but they appear to 

 be indifferently one or the other. The internomedian and anal veins divide between them 

 very equally the inner margin of the wing, the anal furrow being distinct, generally curved 

 considerably and, from the great breadth of the wing, having its general course very 

 oblique ; the internomedian vein generally has but three or four blanches, but several of 

 these usually fork close to the base, the branches redividing, so that rarely less than nine 

 or ten branches of this vein strike the margin, the first offshoot of the penultimate branch 

 often having several inferior veinlets; the vein begins to branch at nearly the same point 

 as the scapular vein, and occupies a subtriangular area with its spreading branches. The 

 branches of the anal vein are in general more longitudinal than those of the internome- 

 dian vein, are nearly parallel, often forked and rather regular and abundant, but in one 

 species are irregular and connected by cross branches. 



The wings are peculiar for their unusual breadth at base and, so far as known, their 

 tapering apex, produced mostly by the costal curve ; the greatest breadth lies before the 

 middle of the wing, and their length is hardly more than double their width, in which 

 particular they differ greatly from Lithomylacris. They have a form common in recent 

 Blattariae, such as Nyctibora, strongly tapering posteriorly, with convex anterior and 

 posterior margins. 



This genus differs principally from Lithomylacris by the form of the wing and by the 

 obliquity of the anal furrow of the same ; and from Necymylacris by the much greater 

 breadth and longitudinal extent of the areas covered by the mediastinal and scapular veins, 

 accompanied by a corresponding diminution of the extent of the externomedian area. The 

 species are all of a rather small or moderate size and are found only in the new world. 



The only fragment apart from front wings which has been discovered is a pronotal shield, 

 presumably belonging to one of these species. It is shaped much as in the modern 

 Periplaneta. 



Mylacris bretonense. PI. 5. fig. 1. 



Bluttlna bretonensis Scudd., Can. Nat., vn, 271-72, fig. 1. Figured also in Dawson's 

 Acadian Geology, Suppl. to 2d ed., p. 55, fig. 5. 



The front wing has a pretty regularly tapering ovate outline, with a slightly produced 

 but rounded tip; the costal margin is apparently regularly and considerably convex, 

 especially near the base, and at least the middle third of the inner margin is straight, while 

 the apical third of the wing tapers about equally from both sides. The veins appear 

 to originate from a point scarcely above the middle line of the wing, and together to be 

 directed considerably upward at base, following the strongly arcuate basal curve of the 



MEMOIRS UOST. SOC. NAT. HIST. VOL. III. 6 



