COPEPODS OF THE WOODS HOLE EEGION 417 



mented, of second and third pairs 3-segmented, exopod of fourth pair 

 3-segmented, endopod 2-segmented ; fifth leg rudiments present in the 

 male; a furca present but no maxillary hook. One species. 



ELYTROPHORA ATLANTICA, new species 



Plates 1, d; 25 



Occurrence. — Twenty specimens, including both sexes, were ob- 

 tained from the gills of the horse mackerel {Thimmis thynnus) at 

 Woods Hole, July, 1915. One of these, a female, has been selected 

 as the holotype with U.S.N.M. No. 56623. The others become para- 

 types with U.S.N.M. No. 56601. 



Color. — Carapace grayish w^hite, with small pigment spots irregu- 

 larly scattered over the dorsal surface; genital segment orange-yel- 

 low ; egg strings gray ; eye reddish brown. 



Female. — Carapace orbicular, a little wider than long, with 

 strongly convex lateral margins, the posterior lobes short and broadly 

 rounded, the median lobe squarely truncated. The furrowing of the 

 dorsal surface of the carapace is different from that in the species 

 already described ; the central area is trapezoidal, widest anteriorly, 

 with sharply rounded anterior corners, straight sides and a concave 

 posterior margin. From each anterior corner a curved groove runs 

 forward, outward, and then backward parallel with the lateral margin 

 of the carapace. The center of this central area projects forward as 

 a rounded knob, with the eye just in front of it. Each lateral area 

 is divided by a transverse groove, which joins the central area at its 

 posterior corner. The fourth segment forms a short narrow waist 

 anteriorly, and is covered posteriorly by a pair of elliptical dorsal 

 plates, or wings, inclined toward each other and overlapping at their 

 tips; the outer margin of each plate is invaginate near its center. 

 Genital segment barrel shaped, with broad posterior lobes curved 

 inward over the basal abdominal segment ; as in the species hemiptera 

 these lobes are separated from the rest of the segment by distinct 

 grooves, and are darker in color. The abdomen is 2-segmented, the 

 basal segment longer than the terminal, with tiny lobes at its pos- 

 terior corners. The caudal rami are shorter than the anal segment, 

 nearly as wide as long, each tipped with three nonplumose setae. 



The frontal plates are narrow and project but little; the second 

 antennae are large and stout; the terminal claw is turned back against 

 the ventral surface of the head and curved sharply near its tip, with 

 a long seta on the outer margin. The second segment also carries a 

 spine on its ventral surface, and the two basal segments are fully as 

 long as the apical claw. The maxilla is stout, simple, and slightly 

 curved; the strong apical claw of the maxilliped is bent into a half 

 circle, the point shutting down against the basal segment. The furca 



