294 BULLETIN" 15 8, UNITED STATES NATIONAL MUSEUM 



Mo^e. — Smaller than the female and not so much depressed; 

 urosome longer and narrower; inner apical seta of caudal rami a 

 little elongated. First antennae hinged between the last two seg- 

 ments, which are considerably elongated; three pairs of aesthetasks 

 as in the female. Fifth legs like those of the female, but a little 

 shorter and narrower, the distal segment only twice the length of 

 the basal segment; a pair of minute finger processes, each tipped 

 with a single seta, representing the sixth pair of legs, are found on 

 the posterior margin of the genital segment. Total length, 0.4— 

 O.T mm. 



Re7nm'ks. — This species is evidently pelagic rather than littoral, 

 and is to be sought in the ocean to the south and the east of Woods 

 Hole. Although it is widely distributed, as shown above, it does 

 not seem to be abundant anywhere. It may be identified by the 

 epimeral plates of the anterior metasome segments, by the very 

 short apical setae on the caudal rami, and by the form of the fifth 

 legs. 



Genus TACHIDIUS Lilljeborg, 1853 



Body short and subdepressed, the metasome much wider and 

 longer than the urosome ; head fused with the first segment ; rostrum 

 large but not defined at its base; urosome 4-segmented in female, 

 5-segmented in male ; genital segment imperfectly divided in female, 

 not divided in male; caudal rami short and wide, apical setae half 

 the body length. First antennae 6- or 7-segmented, enlarged and 

 subchelate in male; exopod of second antenna 2-segmented; rami 

 of first four pairs of legs 3-segmented, second and third pairs modi- 

 fied in male; segments of fifth legs fused into a single wide lamella. 

 One ovisac. 



KEIY TO THE 8PBX!IES (BOTH SEXES) 



1. Basal segment of first antenna divided posteriorly to its center ; 



fifth legs with 4 setae in female, 3 in male littoralis (p. 294) 



Basal segment of first antenna with only a shallow posterior 



notch ; fifth legs with 9 setae in female, 7 in male brevicornis (p. 296) 



TACHIDIUS LITTORALIS Poppe 



FiGUKB 180 



Tachidius littoralis Poppe, Abh. Nat. Ver. Bremen, vol. 7, pt. 2, p. 149, pi. 6, 

 1881. 



Occwrrence. — Found by Williams during April and May in the 

 upper part of Narragansett Bay, Rhode Island. 



Distribution. — Brackish pools, British Isles (Brady, T. Scott) ; 

 Gulf of Suez (Thompson and Scott) ; on seaweed in Ems River, 

 Germany (Poppe). 



Color. — Unknown. 



