49 



acquainted with A. unilineafum, Walk. A. rubigimsum, though found in New 

 England and as far west as Illinois, appears to be most numerous in the oak- 

 lands from Maryland to Tennessee. A. alutaceum is a New England species, 

 and in the West (Missouri, Kansas, and Nebraska) appears to be replaced by 

 A. emarginatum, the two being very closely allied. A. americanum is a 

 southern species, extending as far north as Maryland and lUinois. 



Tropidacris dux, the giant of the family (for Scudder's T. rex is but a 

 variety of this species), belongs to the tropics, and is included in our fauna 

 upon the authority of Mr. Scudder that he possessed a specimen from Texas. 



Rho77ialea centurio {R. marci is probably but a variety of this species) is 

 a southern form extending north in the Atlantic States to North Carolina 

 (possibly to Virginia), and in the Mississippi Valley to Missouri. Walker's 

 R. gigantea from Missouri is evidently R. centurio. 



I add here a table for the purpose of aiding in the determination of the 

 United States genera. It is made as simple and concise as possible, and will 

 require but little study even on the part of the youngest entomologist to un- 

 derstand it. It is artificial, and, as a matter of course, no attempt is made in 

 it to retain the genera in their natural order. I have endeavored in it to 

 seize upon the most prominent distinguishing characters of the genera. 



Synoptical table of the United States genera. 



' I. Pronotum not extending back to the tip of the abdomen ; pulvilli 

 present between the claws of the tarsi : 

 A. Piosternum spined: 



a. Pronotain strongly crested ; crest notched ; insects very 



large, more than three inches long T Tropidacris, 



aa. Pronotum not cristate; species of various sizes, but 



none three inches long : 

 h. Auteuna;. acuminate ; joints distinct : 



c. Head produced in front ; face very oblique : 



d. Pronotum cylindrical ; without lateral carinas ; joints of 



the antenna} flat or triquetrous Mesops. 



dd. Pronotum somewhat compressed on the sides ; lateral 

 carina; more or less distinct ; joints of the antenna', flat 

 or triquetrous Opomala. 



cc. Head not produced; face sub-vertical; joints of the an- 

 tenna; sub-cylindrical Bhomalea. 



hh. AntenniB filiform ; joints indistinct : 



c. Front border of the pronotum notched Ghromacris. 



cc. Front border of the pronotum not notched : 



d. Wings as long or longer than the abdomen : 



7 A 



