84 TETTIGID.E OF NORTH AMERICA 



resembles closely; the form of the body is shorter and more 

 depressed, the humeral angles more jjronounced, the vertex 

 less projecting, and the tegminal sinus less frequently shallow 

 than in typical acadicus (Morse). 



Locality, Colorado, Denver, Poudre River. 



Tettix crassus, Morse, J. N. Y. Ent. Soc, VII., 201 

 (1899); Scudd., Cat. Orth. U. S., 16 (igoo); Scudd., Index 

 N. Am. Orth., 317 (1901). 



Types of this species were examined by the author. 



ARENOSUS GROUP. 



In the form gibbosus is centered a most curious evolution 

 of structures which have involved the arenosiis group in obscu- 

 rity. These changes consist of certain modifications of the 

 pronotum, presenting a more or less abbreviation of that struc- 

 ture, with the wings coincident with general broadening, more 

 flattening, or even depressed, condition of the dorsum between 

 the shoulders and posteriorly between the carinas. Anteriorly 

 before the shoulders there appears more decided constriction, 

 elevating this part of the dorsum into a gibbose eminence; 

 the median carina of the pronotum being low, indistinct, and 

 often formed into slight undulations posteriorly behind the 

 gibbose elevation; this latter condition more particularly 

 characterizes the variety fiuctuosus. Correlative with these 

 modifications is the more projecting character of the frontal 

 facial costa and its more or less distinctly sinuate profile. 

 Leaving these types of variation, it is found on the other hand 

 there is a disposition to greater simplification of structural 

 changes in another direction, especially as regards the pro- 

 notal structures, causing the forms to approach in certain 

 respects the ornatits group. There is less tendency to the 

 gibbose type, with the substituting of a simple and more 

 even elevation of the dorsum between and before the shoul- 

 ders. A series of several hundred specimens arranged before 

 the author suggests these remarks, showing these variations 

 in different stages, which, if taken singly, are not sufficiently 

 differentiated to allow of taxonomic expression. It is in these 



