172 ORTHOPTERA. 



may be included in three large groups or genera ; viz. Acry- 

 dium (of Geoffroy and Latreille), Locusta (^Gryllm Locmta 

 of Linnaeus), and Tetrix (of Latreille). These three genera 

 may be distinguished from each other by the following 

 characters.* 



1. Acrydvj,m. The thorax (p-othorax of Kirby) and the 

 wing-covers of ordinary dimensions ; a projecting spine in 

 the middle of the breast; and a little projecting cushion 

 between the nails of all the feet. 



2. Locusta. The thorax, and usually the wing-covers also, 

 of ordinary dimensions ; no projecting spine in the middle of 

 the breast ; cushions between the nails of the feet. 



3. Tetrix. The thorax (prothorax') greatly prolonged, 

 tapering to a point behind, and covering the whole of the 

 buck to the extremity of the abdomen ; wing-covers exceed- 

 ingly minute, consisting only of a little scale on each side of 

 the body ; fore part of the breast forming a projection, like a 

 cravat or stock, to receive the lower part of the head ; no 

 spine in the middle of the breast ; no cusliions between the 

 nails. 



* I have not considered it necessary to give, in addition to these, the characters 

 that distinguish them from the other genera of American locusts, which are not 

 found in Massachusetts, but add the characteristics of these genera in this note. 



Opsomala. Body slender and cylindrical; head long and conical, extending 

 with an obtuse point between the antennas; eyes oblong oval and oblique; anten- 

 nas short, flattened, and more or less enlarged toward the base, and tapering 

 toward the point; a pointed tubercle between the fore legs on the breast; wing- 

 covers narrow and pointed ; face sloping down toward the breast, and forming an 

 acute angle with the top of the head. 



Truxalis. Body rather thicker; head shorter, but ending in a blunt cone be- 

 tween the antennas; eyes oval and oblique; antennae short, flattened, enlarged 

 near the base, and tapering to a point; no tubercle between the fore legs; wing- 

 covers wider and not so pointed ; face sloping toward the breast, and forming an 

 angle of forty-five degrees with the top of the head; thorax flat above, and marked 

 with three longitudinal elevated lines. 



XijiMcera. Robust; head not conical, but with a projection between the an- 

 tennte ; face vertical ; antennse rather short, flattened more or less, and tapering at 

 the end; a spine between the fore legs on the breast; wing-covers about as long as 

 the abdomen, obtuse or notched at the end; thorax with three elevated crested 

 lines, which are frequently notched. 



Romnlea. Very thick and short; head obtuse; face vertical; antennae short, of 

 equal thickness to the end, seventeen or eighteen jointed; thorax with a some- 



