40 STUDIES IN AMERICAN TETTIGONIIDAE (oRTHOPTERA) 



toward the base (davisi), the lateral portions ranging from 

 sublanceolate (americanus) to rotundate-rectangulate. In da- 

 visi the depth of the division of the plate is somewhat variable 

 but the form is constant. 



Notes on Pronotal Disk. — The disk of the pronotum is slightly 

 different in the two sexes of the same species, in the female 

 averaging more elongate with the caudal margin more truncate 

 than in the male. This difference is, however, in large part 

 nullified or at least modified by the character of variation found 

 in both sexes. There is a very great amount of variation in 

 the general form and proportions of the disk in at least three 

 groups of species (A, B and C), or those with strangulate pro- 

 notal disks, this being purely individual, irrespective of sex and 

 often the extremes are found in material taken at the same time 

 and at the same locahty. We find by measuring the greatest 

 length, greatest caudal width and the least (at cephalic third) 

 width of the disk we have three proportions no two of which seem 

 to correlate with the third. In other words, two specimens 

 of a series may show the same ratio of greatest width of disk 

 to length of same, yet their least width will show no correlation 

 to the other percentage but instead give widely different ratios. 

 In a given species, by taking either of the width measurements, 

 we find their extremes linked up by connecting intermediates 

 of approximately the same disk length, so that there is no true 

 dimorphism, but instead a wide range of variation in dimension 

 of two portions of the same surface, yet these variations show 

 no correlation. 



General Morphological Notes. — In the present genus we find 

 an interesting morphological condition to which attention has 

 been called by Caudell, who found it present in the related 

 genus Eremopedes."^ The presence or absence of prosternal 

 spines has been used by most authors as an important group 

 character for separating genera in the Decticinae, but as Caudell 

 has shown in regard to Eremopedes, and as we find in the present 

 genus, these spines are not to be relied upon as invariable cri- 

 teria. In certain species of the present genus {davisi, monticola 

 and americanus) the spines may be represented by the merest 



^Troc. U. S. Nat. Mus., xxx'i, pp. 330 to 331, (1907). 



