310 BULLETIN" 15 8, UNITED STATES NATIONAL MUSEUM 



ment of the first endopod has a slender apical spine and a stouter one 

 on the inner margin, nodular and blunt at its tip. Between the first 

 legs on the midline is a rounded protuberance, tipped with two 

 spherical processes in contact with each other. The three following 

 pairs of legs are like those of the female; the fifth legs are fused 

 into a lamina shaped like the letter U, each branch tipped with two 

 stout and short spines, curved outward. There are no lateral setae, 

 but instead a pair of minute spines on the surface of the lamina 

 near the base of the U. Total length, 0.3-0.4 mm. 



Remarks. — This species swims with a short jerky motion and usu- 

 ally sticks to the algae and debris, but is rarely captured in open 

 water. It is often entirely covered with colonies of a ciliate belonging 

 to the genus Zoothamnium^ closely related to Stentor. 



Gurney ^ has discussed at some length the synonymy of the differ- 

 ent species in the genus Metis and has decided that Sharpe's species 

 sarsi is a synonym of Richard's jousseau^nei, and that Williams's 

 species 7iatans is valid. Both of these decisions appear to be correct 

 and are here adopted. 



Suborder CYCLOPOIDA 



Fifth thoracic segment forming a movable articulation with the 

 fourth, but firmly attached to the sixth segment. Metasome much 

 wider than the urosome and more or less depressed. Eggs carried 

 in two ovisacs, which are attached to the lateral or subdorsal surface, 

 but never to the ventral surface as in the suborder Harpacticoida. 

 Anterior antennae elongate and usually composed of a greater num- 

 ber of segments than those of the Harpacticoida, but not so great as 

 those of the Calanoida. Posterior antennae generally simple, the 

 exopod obsolete, the only exceptions being found in parasitic forms. 

 First four pairs of swimming legs well developed, with stout seg- 

 mented rami, the exceptions again being certain females of parasitic 

 species. Fifth legs small and simple and alike in the two sexes. 



Remarks. — This group includes species living in fresh, brackish, 

 and salt water, and also comprises free swimmers, commensals, and 

 parasites. As in the previous groups the number of segments in the 

 rami of the swimming legs is not always the same for all the species 

 of a given genus, and hence some genera appear twice or more in the 

 key (Appendix B, p. 583). Owing to the presence of a movable 

 joint between the fourth and fifth thoracic segments, the latter 

 might be considered at first sight to be a part of the urosome. It 

 seems far preferable, however, that the terms metasome and urosome 

 should retain exactly the same significance in each of the various 



» Trans. Zool. Soc. London, pt. 4, 1927, pp. 567, 568. 



