COPEPODS OF THE WOODS HOLE REGION 237 



and squarely truncated at its tip, where it carries three stout setae, 

 the outer one much the thickest and longest; there is also one stout 

 seta on each lateral margin. The distal segment is as wide as long 

 and obliquely truncated, with three stout setae on the oblique margin, 

 the middle one much the longest, and a filiform seta on the anterior 

 surface near the base of the long middle seta. Total length, 

 0.5-0.65 mm. 



Male. — A little smaller than the female, with a more prominent 

 rostrum ; urosome 5-segmented and as long as the metasome ; caudal 

 rami twice as long as wide, with very long apical setae, which are 

 entirely separated at their base. First antennae with the third seg- 

 ment considerably swollen and armed with a short and club-shaped 

 aesthetask, the apical segment subspherical and tipped with two 

 short claws. Second antennae, mouth parts, and swimming legs 

 like those of the female; fifth legs smaller, the distal segment as 

 long as the basal expansion, with four slender and weak setae, the 

 basal expansion with three still smaller setae. Total length, 

 0.^0.5 mm. 



Rertiarks. — This is the first record of this species outside of New 

 Mexico, where it was found in fresh and brackish waters. Her- 

 rick's diagnosis of his new genus Marshia^ founded on this and 

 another species, and his descriptions of the two species were filled 

 with errors, especially with regard to the five pairs of legs. Endo- 

 pods and exopods were transposed in every instance, and although 

 the fifth legs show no visible segmentation, their form shows con- 

 clusively that they are composed of two segments fused. Marsh, 

 in his Fresh-water Biology, 1918 (p. 780), corrected some of these 

 statements, but no revised description has ever been published. For 

 this reason a longer description has been given here, with figures 

 of the female, since nearly all Herrick's figures of this species were 

 from the male. 



Genus MESOCHRA Boeck, 1865 



Body of medium length, tapered posteriorly, with but little dif- 

 ferentiation between metasome and urosome; head fused with the 

 first segment and much shorter than the rest of the metasome; 

 rostrum broadly triangular and bluntly rounded; urosome 4-seg- 

 mented; genital segment with only lateral indications of division; 

 caudal rami short and truncated. First antennae 6- or 7-segmented ; 

 exopod of second antennae 1-segmented, minute; exopods of first 

 four pairs of legs 3-segmented, endopods 2-segmented, proximal seg- 

 ments well developed ; first legs prehensile, the endopod longer than 

 the exopod and often 3-segmented; fifth legs 2-segmented, of 

 the usual pattern. 

 71937— 3S ^17 



