90 BULLETIN 15 8, UKITED STATES ^-ATIONAL MUSEUM 



Bases of mouth parts dark, becoming transparent toward their tips; 

 antennae, swimming legs, and caudal rami transparent; eye claret 

 red (Eathbun). 



Female. — Body smaller and more slender than in the preceding 

 species; posterior corners of fifth segment less expanded, the spines 

 shorter, the right one turned outward instead of backward; genital 

 segment only slightly asymmetrical, finely ciliated along the sides, 

 with a recurved spine on the ventral surface in front of the genital 

 orifice ; spine on inner margin of second exopod segment of fifth legs 

 not half the length of the end segment ; caudal rami about three times 

 as long as wide. Total length, 1-1.35 mm. 



Male. — Smaller than the female ; posterior corners of fifth segment 

 symmetrical ; urosome half the length of the metasome ; first antennae 

 without dentiform processes on the anterior margin of any of the 

 segments, the right antenna not swollen so much as in typicus; chela 

 on fifth leg less powerfully developed, not reaching the caudal rami, 

 the thumb a simple spine, shorter than the finger, and both very 

 acuminate. Total length, 0.9-1.2 mm. 



Remarks. — Wheeler found this species present in considerable num- 

 bers in the tow taken from the Bureau of Fisheries wharf at Woods 

 Hole in July and August. Fish recorded it as one of the three cope- 

 pods characteristic of winter plankton in Woods Hole Harbor, and 

 said that the young become so abundant in January and February 

 that they far outnumber the adults. 



Family DIAPTOMIDAE 

 Genus DIAPTOMUS Westwood, 1836 



Body slender, with a well-defined cervical depression across the 

 center of the dorsal surface of the head; fourth and fifth segments 

 imperfectly separated, the posterior corners biangular, with a minute 

 spine at each angle; urosome 3-segmented; caudal rami much longer 

 than wide ; exopod of second antennae longer than endopod ; rami of 

 first 4 pairs of legs 3-segmented, except the first endopod, which is 

 2-segmented ; exopod of fifth legs in female with a distinct terminal 

 segment, carrying two spines; exopod of right fifth leg in male 

 tipped with a long curved and denticulated claw ; egg case single and 

 ventral. 



Remarks. — This genus has been but little investigated in New Eng- 

 land. De Guerne and Kichard in 1889 reported two species in the 

 United States east of the Appalachians, minutus and leptopus. To 

 these Marsh added in 1907 oregonensis from eastern Massachusetts, 

 hirgei from Cold Spring Harbor on Long Island, N. Y., and spatulo- 

 crenatus from Wigwam Pond, Nantucket, Mass. Forbes has reported 



