238 NORTH AMERICAN OEDIPODINAE (ORTHOPTERA; ACRIDIDAE) 



as described to nearly straight, while the lobe angles vary in the 

 extent to which they are rounded. The caudal femora have the 

 depth varying from three and one-half to slightly more than four 

 times in the length. The caudal tibiae have from seven to nine 

 external, and from eight to twelve^" internal marginal spines. 



At Mason the species occurred on a gravelly alluvial slope with 

 fairly heavy but scattered bush vegetation, and also in a depres- 

 sion of the slopes with similar cover. The species was scarce in 

 the former situation, and more numerous, but not common, in 

 the latter location. At Mina the insect occurred in but one en- 

 vironment, this was on ground strewn with rock fragments, the 

 general location being to the east of the broad playa in the middle 

 of the valley in which Mina is located, and where there is a sim- 

 ilar but sparser vegetation than found at Mason. The species 

 was not common, and individuals were secured only after long and 

 careful search. 



The Plattei Group of the Genus Mestohregma 

 This group is composed of two sections, one comprising plattei 

 and its races and the second composed of impexum and terricolor, 

 both of the latter very distinct new species, here described. 



The races of Mestobregma plattei number three. These are: 

 plattei plattei,^^ which is the form of the Great Plains region, south 

 to southern Colorado; plattei corrugata (Scudder),^- ranging from 

 northern New Mexico southward, and plattei ruhripenne (Bruner)i^ 

 of central and southern Arizona. In our detailed projected 

 study of the genus we will discuss the relationship, synonymy 

 and variation, as well as detailed distribution, of these forms. 



The impexum-terricolor section of the group is moderately 

 cohesive, made up of the two species, which agree in eye outline, 

 and to a certain degree in pronotal form, but differ in the form 

 of the frontal costa, fastigio-facial angle, mesozonal carina, lengtii 

 of lateral lobes and general form. Impexum is nearcn- plattei than 

 terricolor, and the latter is an evident tendency toward Trepidulus, 

 yet in all general features it is a true Mestobregma. 



" The latter on one margin in tyf)e only. 



11 1873. Oe{dipoda) 'plattei Thomas, Rep. U. S. Oeol. Surv. Terr., v. p. 123. 

 ["Near Platte River in Colorado and Wyoming."'] 



'2 1902. Conozoa corrugata Scudder, in 8cndder and Cockerell, Proc. Davenp. 

 Acad. Sci., ix, p. 33. [Fillmore Canyon, Organ Monntains, New Mexico.] 



'•■' 190.'). Tnichyrhachis rubripennis Bruuer, Biol. Cent.-.Amcr., Orlh., ii, 

 pp. 17.3, 177. [Oracle, Arizona.] 



