NO. 1504. AMERICAN PARASITIC COPEPODS— WILSON. 681 



better to wait for further material before establishing a new species. 

 But after a personal examination of the present specimen its identity 

 as a new species is so apparent that the author considers Rathbun 

 full}^ justified in making of it a new species without waiting for more 

 specimens. 



It is Cat. No. 6193, U.S.N.M., and was taken from a sting ray cap- 

 tured in Vineyard Sound, Massachusetts, by the United States Fish 

 Commission in 1871. 



TREBIUS CAUDATUS Kroyer. 



Plate XV, figs. 11-13; Plate XVI, figs. 14-22; fig. 1, p. 673. 



Trebius caudatus Kroyer, 1838, p. 30, pi. i, fig. 4. — M. Edwards, 1840, p. 458. — 

 Baird, 1850, p. 280, pi. xxxiii, figs. 3 and 4.— KrOyer, 1863, p. 149, pi. x, 

 fig. 1 a-A-.— 0L.SSON, 1869, p. 14, pi. i, figs. 3 and 4.— Thomrson, 1888, p. 69, 

 pi. II, fig. 10.— T. Scott, 1900, p. 155, pi. vi, figs. 20-26. 



Female. — Carapace orbicular, a little longer than wide, somewhat 

 contracted anteriorly and well arched dorsally. Frontal plates nar- 

 row and only two-tifths the width of the carapace. Transverse grooves 

 separating the cephalic and thoracic portions of the lateral areas far 

 back, leaving the thoracic portion much the shorter of the two. Eyes 

 not showing in the adult but visible in the young as two purplish-red 

 spots, not fused but close together and about one-third the distance 

 behind the anterior margin. Third thorax segment one-half wider 

 than the fourth, but not as long; fourth segment spindle-shaped, being 

 widened considerably between the bases of the fourth legs. 



Genital segment enlarged to about three-fifths the size of the cara- 

 pace, Hask-shaped, the anterior end narrowed into a sht)rt neck where 

 it joins the fourth segment. The posterior corners are evenl}' rounded 

 and armed on the dorsal surface with three or four stout, broadly tri- 

 angular spines which project over the bases of the egg-strings. The 

 latter are usually a little longer and about the same width as the abdo- 

 men. Sometimes, as in one of Kro3^er\s two original type specimens, 

 the Qgg strings are not as long as the abdomen. Eggs quite small, 

 from 30 to 40 in each string. 



Abdomen one-half longer than the genital segment and only three- 

 eighths as wide; three-jointed, the joints diminishing greatly in length 

 and slightl}" in width from the base toward the tip. 



Anal laminse short and narrow, each armed with four small plumose 

 setcT, of which the outer and inner ones are the shortest. 



Second antennae with the two basal joints thick and stout, the ter- 

 minal claw long, slendei', and not more than one-tifth as wude as the 

 basal joints. First maxilla^ long for a female, thick and stout, with 

 the base swollen into a transversely elliptical form. Second maxillfe 

 elongate-triangular, with the basal joint fused to the ventral surface 



