12 FURTHER RESEARCHES ON NORTH AMERICAN ACRIDIIM. 



As nearly as may be judged from the limited material at hand, 

 several so-called species of Trachyrhachis founded largely upon color- 

 characters (thomasi, fuscifrons, obliterata, kiowa) are to be regarded 

 simply as geographical varieties or races of a widely spread species 

 varying with the climatic environment. Thus, T. thomasi, the form 

 inhabiting the more eastern and humid section of its range (Georgia, 

 Tennessee, Illinois, Arkansas, Indian Territory), possesses wings with 

 a complete, rather broad, transverse fuscous band and lemon-yellow 

 disk; fuscifrons, from more western and less humid localities in Texas 

 and Oklahoma, exhibits a narrower, usually broken wing-band and 

 yellow disk, the latter sometimes nearly hyaline; in obliterata the 

 wing-band is reduced to faint cloudings in the radial and posterior 

 parts of its course or is frequently lacking (this form is found in the 

 semi-arid parts of central and western Texas and Oklahoma); kiowa, 

 lacking the wing-band entirely and with hyaline disk, is the charac- 

 teristic form at Amarillo on the Staked Plains. We apparently have 

 in this instance another case of increased development of pigment 

 correlated with humid conditions. Further observations should be 

 made on material in large series. (See also p. 37.) 



Variation in color and structure geographically along the lines of 

 probable dispersal and descent is exhibited by Hesperotettix pratensis. 

 Examples of this species from Magazine Mountain, Arkansas, are 

 shorter-winged than plains specimens and exhibit almost exactly the 

 type of coloration shown by H. brevipennis. The specimens of the 

 latter species from Georgia and Alabama approach in size, wing- 

 length, and color the Arkansas examples of pratensis. It is probable 

 that complete inter gradation will be found to exist, and that H. brevi- 

 pennis is the eastern representative of pratensis, directly descended and 

 not specifically distinct from that species. The Florida examples of 

 H. pratensis secured in 1903, on the other hand, present a distinctly 

 different type of coloration one seen in some Californian series of 

 the species. They are also of small size like them, but differ in having 

 much longer tegmina and wings. H. pratensis, as it stands to-day, 

 should be regarded as a variable and complex species represented in 

 different parts of the country by several more or less distinct varieties. 



The same phase of variation (along the line of dispersal and 

 descent) is probably the explanation of the striking difference shown 

 in examples of Trimerotropis saxatilis from Stone Mountain, Georgia, 

 and Mount Sheridan, Oklahoma. But for the intergrades from 

 Arkansas and identity of habits these two forms would be regarded as 

 specifically distinct on the basis of structural characters. In this 

 case Trimerotropis vinculata, very widely distributed in the far west, 

 is probably the parent species. 





