172 
ORTHOPTERA. 
may be included in three large groups or genera; viz. Aery- 
dmm (of Geoffroy and Latreille), Locusta (^Gryllus Locusta 
of Linnaeus), and Tetrix (of Latreille). These three genera 
may be distinguished from each other by the following 
characters.^ 
1. Acrydium. The thorax (^pvthorax of Kirby) and the 
wing-covers of ordinary dimensions ; a projecting spine in 
the middle of the breast; and a little j^rojecting 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 
back 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 cushions 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 antennte; eyes oblong oval and oblique; anten¬ 
nae short, flattened, and more or less enlarged toward the base, and tapering 
toward the poiiit; 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. 
Truxalls. Body rather thicker; head shorter, but ending in a blunt cone be¬ 
tween the antennae; 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. 
Xiphicera. Robust; head not conical, but with a projection between the an¬ 
tennae; face vertical; antennae 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. 
Romalea. Very thick and short; head obtuse; face vertical; antennae short, of 
equal thickness to the end, seventeen or eighteen jointed; thorax with a some- 
