PARASITIC COPEPODS— WILSON. 395 



d. Frontal plates projecting as a semicircular rostrum between the antennoe; 

 sinuses between the dorsal plates very deep and slit-like; sixth segment 



plate half the width of the genital segment xmicolor Hesse, 1883, p. 31)0. 



d. Frontal plates projecting as a semicircular rostrum between the antenna'; 

 lateral plates of second segment linear; sixth segment plate only one-fourth 



the width of the genital segment carcharii-glaucus Hesse, 1883. 



d. Frontal plates scarcely projecting; frontal margin straight; plates on sec- 

 ond segment as wide as those on third; sixth segment plate three-fifths the 



width of the genital segment Mcolor Leach, 1816, p. 400. 



€. Dorsal plates on the free and genital segments approximately the same size; 



carapace wedge-shaped, not much narrowed anteriorly /■ 



e. Dorsal plates quite unequal, at least one pair much enlarged or diminished; 



carapace much narrowed anteriorly, with strongly convex sides g. 



f. Frontal plates very narrow, especially on the mid line; dorsal plates <m 



third and fourth segments more than twice as wide as long 



cranchii Leach, 1819, p. 403. 



/. Frontal plates wide, and widest at the center; dorsal plates on third and 



fourth segments al)out the same width and length, each armed with a 



stout spine on the dorsal surface armahts Helkr, 1865. 



g. Plates of third segment much diminished and completely separated on the 

 mid line; the other median sinuses deep and acute; plates on fourth and 



genital segments equal lugubris Heller, 1865. 



g. Plates of fourth segment much enlarged, nearly covering the genital segment; 

 sinus between plates of third segment deep, often separating them entirely; 



other sinuses shallow; sixth segment plate strongly narrowed at its base 



smUhii Rathlnin, 1886, p. 410. 

 g. Plates of genital segment enlarged, the others nearly e(iual; all the median 

 sinuses very shallow; sixth segment plate as long as genital segment, nar- 

 rowed but slightly at its base satyrus Dana, 1852, p. 415. 



g. Plates of fourth and genital segments enlarged, with broad and shallow sinuses; 

 sinus between plates of third segment narrow and much deeper; sixth segment 



plate strongly narrowed at its base sinudtus Say, 1817, p. 417. 



h. Carapace longer than wid^; free segments all as wide or wider than the 



genital segment; abdomen wider than long i- 



h. Carapace wider than long, the lateral margins strongly curved; fourth 

 segment narrower than genital segment; aV)domen decidedly longer than 



wide *^- 



i. Carapace elliptical, strongly narrowed anteriorly and posteriorly; eyes dis- 

 tinctly visible; exopod of first legs twice the size of the endopod 



brcvicaudis Dana, 1852, p. 397. 

 i. Carapace orbicular, not visibly narrowed; eyes invisible; rami of first legs 



about equal; only one pair of adhesion pads, at base of first antennae 



smithii Rathbun, 1886, p. 410. 

 k. Length of carapace on mid line only one-third the entire length; Iwth 



fifth and sixth legs large and prominent, triangular, and acuminate 



cranchii Leach, 1819, p. 403. 

 k. Length of carapace on mid line two-fifths the entire length; fifth and 



sixth legs both small, inconspicuous, and V)luntly rounded 



simiatus Say, 1817, p. 417. 

 h. Length of carapace on mid line three-eighths the entire length; sixth 



legs much smaller than the fifth and hardly visible 



bicolor Leach, 1819, p. 400. 



