ART. 5. NOETH AMERICAN PARASITIC COPEPODS WILSON. 83 



5. Head smooth ; trunk three times as long as wide, witli rudiments of third 

 and fourth legs on its margins 1.60 mm., subpinguis Brian, 1913 



5. Head smooth; trunk five times as long as wide; first antennae two-jointed; 



no legs visible dorsally 1.75 mm., mulli (Beneden), 1851 



6. Trunk as wide as or wider than the head and only twice as long or less, 



short and stout species 7 



6. Trunk three or four times the length of the head and the same width or less, 



longer and narrower species 8 



7. Head a quarter wider than long; trunk one-half wider than the head, with 



two lateral sinuses on each side ; egg strings at right angles to body axis ; 

 first antennae five-jointed 1 mm., uncata Wilson, 1913 



7. Head a third wider than long; trunk not as wide as head, with a single 

 sinus on either side ; egg strings nearly parallel with body axis ; first 

 antennae four-jointed 2.75 mm., indescens Wilson, 1913 



7. Head the same width and length ; trunk a fifth wider than the head, with 

 three sinuses on either side, containing rudiments of a third and fourth pair 

 of legs ; antennae five-jointed 0.85 nun., insolita Wilson, 1913 



7. Head wider than long, trunk a half wider than the head, without sinuses; 



egg strings twice the entire length 1.80 mm., pinyiiis Wilson, 1908 



8. Head winged on either side, so as to be wider than long; first antennae 



twelve to twenty jointed 9 



8. Head winged but fully as long as wide; first antennae short, only five to 



eight jointed 10 



9. Head large, triangular, widest at anterior margin ; two free segments only 



a fifth the length of the head ; genital segment pointed posteriorly ; first 



antennae twelve-jointed 2-3 mm., crenilahri (Hesise), 1878 



9. Head widest at the center, transversely spindle-shaped ; two free segments 

 half the length of the head; genital segment rounded posteriorly; first 

 antenna fourteen-jointed 2 mm., labri-mixti (Hesse), 1878 



9. Head widest at the center ; two free segments nearly as long as the head ; 



genital segment uniform in width, rounded posteriorly ; first antennae 

 twelve-jointed 1.50 mm., labri-donovaini (Hesse), 1878 



10. Trunk spindle or club shaped; first and second segments not separated 

 from the trunk 11 



10. Trunk club-shaped or with parallel sides ; first and second segments dis- 



tinctly separated ; both pairs of legs visible dorsally 12 



11. Trunk spindle-shaped, with lateral sinuses and rudiments of the third and 

 fourth legs ; head diamond-shaped. 



1 mm., lahracis (P. J. van Beneden), 1870 



11. Trunk club shaped, larger posteriorly, without lateral sinuses ; head nearly 

 spherical ; no legs visible dorsally 1.50 mm., cluthae T. Scott, 1902 



12. Two free segments half the length of the head; genital segment squarely 



truncated posterioi-ly, with a distinct abdomen and mth its sides con- 

 cave 1.50 mm., acantholabri-exoleti (Hesse), 1878 



12. Two free segments less than a third the length of the head ; genital segment 

 indistinguishably fused with the abdomen and pointed posteriorly, its sides 

 convex 2.30 mm'., lahri-trimaculati (Hesse), 187S 



12. Head almost as long as the rest of the body ; genital segment the same width 

 throughout and squarely truncated posteriorly, 



2 mm., canthari-grisei (Hesse), 1878 



12. Head without lateral expansions; two free segments as long as the head; 

 sides of genital segment straight 3mm., pagelli-bogneravei (Hesse), 1878 



