178 BULKETIN 15 8, UNITED STATES NATIONAL. MUSEUM 



Remarks. — This species can be recognized by the combination of 

 rosy color, strong lateral compression, and elongate caudal setae. 

 It is apparently a surface species and has thus far been taken only 

 in surface tows. 



ARENOSETELLA, new genus 



Body slender and slightly compressed laterally; metasome scarcely 

 wider than urosome; head fused with first segment; rostrum short 

 and deflexed; sides of cephalothorax turned downward, partly cov- 

 ering the mouth parts and the bases of the swimming legs; genital 

 segment not divided ; urosome 4-segmented in female, 5-segmented in 

 male, the anal segment armed on the dorsal surface with a pair of 

 small curved claws, arranged like the jaws of a pair of pliers and 

 working horizontally; caudal rami short, their inner apical setae 

 elongate. 



First antenna 5- or 6-segmented, slender, with a terminal aesthetask 

 as long as the entire antenna; exopod of second antennae 3-seg- 

 mented, the end segment the longest; mandibles with a very large 

 palp, its distal segment spatulate, somewhat bifid at the tip, and 

 armed with exceptionally long setae, its outer ramus rudimentary 

 and destitute of setae. First maxillae simple, with a 2-lobed setifer- 

 ous palp; second maxillae very large and tipped with seven long 

 setae, three of which are denticulate; maxillipeds stout, with two 

 terminal claws and two accessory spines. First four pairs of legs 

 with 3-segmented rami, the endopods longer than the exopods; fifth 

 legs 2-segmented, the inner expansion of the basal segment with two 

 setae, the distal segment 3-lobed, with three setae. A single ovisac. 



Genotype. — Arenosetella syinicauda.^ new species. 



Remarks. — This genus is closely related to Mier'osetella but differs 

 enough in its anatomical details to warrant generic distinction. The 

 two pairs of antennae, the mouth parts, especially the maxillipeds, 

 and the dorsal claws on the anal segment of the abdomen are dis- 

 tinguishing characters. Furthermore, both the known species of 

 Microsetella are pelagic in their habits, being always found at or near 

 the surface. In marked contrast the present genus actually lives 

 within the bottom sand and seldom comes out to swim about freely. 

 Its powers of locomotion are practically confined to crawling about 

 in the sand, and its motion when swimming is sinuous and worm- 

 like, rather than the jerky progress characteristic of most copepods. 



KEY TO THE SPECIES (BOTH SEXES) 



1. Claws on dorsal surface of anal segment simple, separated at 



base, and without accessory spines spinicauda (p. 179) 



Claws on dorsal surface of anal segment bifid, fused at base, and 

 each armed with an accessory spine fissilis (p. ISO) 



