ART. 5. NORTH AMERICAN PARASITIC COPEPODS WILSON. 33 



6. Fourth legs projecting but little beyond the dorsal plate; rami slender and 

 cylindrical 3 rum., female, vorax Richiardi, 18S0 



6. Fourth legs projecting their entire length ; rami flattened into lanceolate 

 laminae 4.50 mm., female, miigilis Brian, 1898 



6. Fourth legs projecting their entire length ; rami slender, cylindrical ; dorsal 



plate divided by a deep longitudinal incision like the wings of a fly, 



8 mm., female, musca Blainville, 1822 



7. Posterior margin of dorsal plate smoothly rounded ; fourth legs not reaching 



this margin female, polynenii Richiardi, 1881 



7. Posterior margin of dorsal plate smoothly rounded ; fourth legs project well 

 beyond this margin 2.25 mm., female, bclones Kr0yer, 1863 



7. Posterior margin of dorsal plate deeply bilobed, the sinus triangular and 



reaching center of plate 3 mm., female, tracliuri Brian, 1903 



8. Posterior portion of dorsal plate the same width as the anterior portion 



or narrower 9 



8. Posterior portion of dorsal plate distinctly wider than the anterior portion_19 



9. Anterior portion of dorsal plate with large lateral wings; fourth legs pro- 



jecting nearly their entire length, 



3.30 mm., female, caudatus, new si)ecies, p. 37 

 9. Anterior portion of dorsal plate with large lateral wings ; fourth legs not 



projecting at all 10 



9. Anterior portion of dorsal plate without wings, but with processes at its 



posterior corners ; fourth legs projecting more or less 11 



9. Anterior portion of dorsal plate without wings or processes ; fourth legs 



projecting moderately 12 



10. Genital segment short and wide, without transverse folds ; fourth legs cut 

 to center, rami slender and acuminate, 



2.50 mm., female, triyonocephahis Heller, lS6o 



10. Genital segment narrow and elongate, with transverse folds ; fourth legs 



cut to their base, rami broad laminae bluntly pointed, the exopod slightly 



the longer 2.75 mm., female, pagelli Kr0yer, 1863 



10. Genital segment narrow and elongate, with transverse folds ; fourth legs cut 

 to their base, rami broad laminae, bluntly pointed, the endopod much the 

 longer 2.25 mm., female, scribae Kr0yer, 1863, p. 40 



11. Fourth legs short, projecting half their length, rami subparallel; no fifth 

 legs 3 mm., female, atrox Heller, 1865 



11. Fourth legs elongate, cylindrical, projecting three-quarters of their length, 

 rami divergent ; fifth legs present ; processes on anterior dorsal plate flaring, 



9 mm., female, giganteus Kr0yer, 1863 



11. Fourth legs not projecting at all ; no fifth legs ; processes closely appressed 

 to the body 3.37 mm., female, quadratus (Kr0yer), 1837 



12. Abdomen wholly or partially visible in dorsal view ; fourth legs visible 

 their entire length 13 



12. Abdomen wholly covered by the dorsal plate ; fourth legs only partly visible, 

 their bases being covered 16 



13. Rami of fourth legs longer than the entire body and acuminate 14 



13. Rami of fourth legs much shorter than the entire body and acute 15 



14. Anterior portion of dorsal plate overlapping the posterior portion and 

 bilobed ; cephalothorax also invaginate at the center of the posterior margin, 



5 mm., female, nudus Basset-Smith, 1898 

 14. Anterior portion of dorsal plate neither overlapping nor bilobed ; cephalo- 

 thorax not invaginate but with its lateral margins curled far over ventrally, 



7.60 mm., female, tenuis, new name, p. 33 



