AMEHKAN ORTHOPTERA. 237 



The .subjoined observations on Illinois grouse locusts are accom- 

 jjanied by original plates. Some evolutionary stages in the mark- 

 ings of Tcffic are shown, and in this genus a feature is the introduc- 

 tion of enlarged sketches of the chephalo-dorsal outline. Ov«r 

 seven hundred specimens in the writer's collection formed the basis 

 of this paper without mentioning the great store of specimens ex- 

 amined in the field alive, nund)ering into thousands. That portion 

 of northern Illinois known as the Des Plaines, and a part of the 

 Calumet River region in Cook County, formed the central focus of 

 observations. So far recorded this grouj) of locusts as found here is 

 given in the accompanying list ; a number are new. Among speci- 

 mens from M. J. P^lrod and Mr. Adams, of Bloomington, 111., to 

 whom the writer expresses obligations, there was one new slender 

 species, described under Tettlx angustm. A series of specimens from 

 S. W. Blatchley, from Vigo County, Indiana, and a nundier from 

 A. P. Morse, of Wellesley, Mass., furnished valuable assistance in 

 making com})ansons. 



Gen. TETTIX Charp. 



1. T. sfi-aniilatut^ Kirby (Plate VI, fig. 3. 3«). 



Cephalo-dorsal outline as shown plate ix, fig. 28. Easily recog- 

 nized by the angulate character of the vertex.* A uniformity of 

 structure is common in specimens taken in Chicago, Riverside, and 

 at Dune Park, Ind. Colors are extremely variable. 



Length of body 9 , 15 mm. ; ?> , 12 mm. 



Abbreviated variety, 9 I '^ single specimen from Chicago and one 

 found at Dune Park, Ind., resembles this form, excepting an abor- 

 tive condition of the wings and pronotum. Wings not passing the 

 hind femora. The vertex, while angulate, hardly advanced as far 

 in front of the eyes. Length of body 9 mm. 



•2. T. wriiatiis Say (Plate VI, fig. 1, In). 



Cephalo-dorsal outline as shown plate ix, fig. 29. Between this 

 and the form triangularis there is no tangible specific difiference. 

 The latter is an abbreviated variety (see plate vi, fig. 2, 2a), and 

 nnich confusion has existed respecting it. In dry open woods in 

 upland country it often takes on the color phase, bilineata of Harris, 

 plate viii, fig. 20. 



Chicago, Riverside and Rivergrove, 111. 



* The Western species is T. incurvatus Hancock. See "American Natui-alist." 

 August. 1895, p. 761. 



TRANS. AM. ENT. SOC. XXIII. JULY, 1896. 



