NO. 1788. NORTH AMERICAN ERGASILID^— WILSON. 327 



which was put forth as a probable synonym of Hesse's Megahrachinus suboculatus, 

 must stand valid until some one can give us confirmation of Hesse's species. 

 a. Head completely fused with the first thorax segment, with no indication of the 

 union; carapace elongate, much longer than wide, and more than half the entire 



length b. 



a. Head fused with the first thorax segment, but the fusion indicated by distinct 

 indentations on the lateral margins; carapace half the entire length and violin 



shaped e 



a. First thorax segment distinctly separated from the head by a well-defined groove; 



carapace short, as wide as long, and much less than half the entire length h. 



b. Anterior margin of carapace evenly rounded; first antennae hardly reaching the 



end of the first joint of the second pair; both rami of fourth legs 3-jointed c. 



b. Anterior margin of carapace projecting strongly at the center in a rounded knob; 



first antennae much longer and heavily bristled d. 



c. Second antennae one-third the entire length; basal joint much swollen and 

 widened distally; second joint with a large process on its outer border. 



funduli Kroyer, 1863, p. 328. 

 c. Second antennae half the entire length, the two basal joints without swellings 



or processes labracis Kroyer, 1863, p. 329. 



d. Second antennae normal; terminal claw simple; both rami of foiu-th legs 3- 



jointed centrarchidarum Wright, 1882, p. 331. 



d. Second antennae normal; terminal claw toothed on the inner margin; exo- 



pods of fourth legs two-jointed caeruleus, new species, p. 334. 



d. Second antennae with large processes in the form of sleeves around the base 

 of each joint; terminal claw with a large tooth on the inner margin; fourth 



exopods 2-jointed manicatus, new species, p. 337. 



e. Both rami of fourth legs 3-jointed /. 



e. Exopod of fourth legs with but two joints g. 



f. Ventral surface of genital segment smooth; three abdominal segments 



the same length sieboldii Nordmann, 1832, p. 338 



/. Ventral surface of genital segment armed posteriorly with a large num- 

 ber of coarse bristles; third abdomen segment much shorter than the 



other two lizse Kroyer, 1863, p. 340. 



g. Second antennae as long as the carapace; the latter much narrowed 

 posteriorly; fifth legs of good size, armed with three setae. 



nanus van Beneden, 1870. 

 g. Second antennae as long as the carapace; posterior portion of latter as 

 wide as anterior; fifth legs reduced to a single small spine. 



versicolor, new species, p. 341. 

 g. Second antennae only half the length of the carapace; posterior por- 

 tion of latter as wide as the anterior; fifth legs reduced to a single 



spine chautauquaensis Fellows, 1888, p. 343. 



h. Head, thorax, and abdomen diminishing regularly in width; cara- 

 pace relatively narrow and evenly rounded anteriorly i. 



h. Carapace relatively wide, with a rounded projection at the center 

 of the anterior margin; first thorax segment as wide as the cara- 

 pace, second abruptly narrowed to half that width j. 



i. Second antennae one-third the entire length; abdomen one-half 

 longer and a little narrower than the genital segment; fifth legs 



short and stout, with a single seta peregrinus Heller, 1865. 



i. Second antennae one-half the entire length; abdomen shorter and 

 much narrower than the genital segment; fifth legs reduced to a 

 mere spine longimanus Kroyer, 1863. 



