168 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 
Islands. Since it has never been recorded elsewhere, this is the first 
Pacific record, as in the case of the preceding species. 
ARIETELLUS PLUMIFER Sars 
PLATE 20, FIGURE 281 
Arietellus plumifer Sars, Bull. Mus. Océanogr. Monaco, No. 40, p. 21, 1905b; Rés. 
camp. sci. Albert de Monaco, No. 69, p. 332, pl. 119, figs. 7-11, 1925. 
Stations 4673; 4700; 4705; 4707; 4717; 4719; 4722; 4730; 4742; 
4743; 5120; 5185. Established by Sars upon specimens of both sexes 
found in the northern Atlantic and does not appear except in the 
Monaco plankton. The list of stations shows that the species is fairly 
abundant in the Pacific. One of the males from station 5120 is 
worthy of notice because of variations in the details of the fifth legs as 
shown on plate 19, figure 281. There is sufficiently close correspond- 
ence to Sars’ figure (pl. 119, fig. 10) of the fifth legs to show that the 
two are really the same species. But there are interesting differences 
in the details of the endopods, the second segment of the right exopod, 
and the terminal segment of the left exopod. 
ARIETELLUS SETOSUS Giesbrecht 
PLATE 20, FIGURES 2838, 284 
Arietellus setosus GIESBRECHT, Fauna und Flora des Golfes von Neapel, monogr. 
19, p. 415, pl. 29, figs. 1, 3-7, 9-13, 21; pl. 39, figs. 34-36, 1892. 
Stations 4638; 4721; 4730; 4734; 4740; 5451. This species has been 
reported in the Stboga, Monaco, and Carnegie plankton lists and is 
well distributed in every ocean. It may be recognized by the length of 
the caudal setae, which often equals that of the entire body. These 
setae are also often tufted and densely plumose; in fact, the plumes 
are so dense that they sometimes become badly matted in the preserva- 
tive. The forehead is pointed and terminates in a short blunt spine. 
The first antennae do not quite reach the tips of the spines at the 
posterior corners of the metasome. 
ARIETELLUS SIMPLEX Sars 
PLATE 21, FIGURE 300; PLATE 22, FicureEs 301, 302 
Arietellus simpler Sars, Bull. Mus. Océanogr. Monaco, No. 40, p. 22, 1905b; 
Rés. camp. sci. Albert de Monaco, No. 69, p. 334, pl. 120, figs. 7-12, 1925. 
Stations 3; 4655; 4673; 4679; 4700; 4707; 4711; 4715; 4717; 4719; 
4740; 4758; 4766; 5120; 5185; 5287. This is the largest species of the 
genus and was found at 1 Stboga and 14 Monaco stations. All the 
Monaco specimens were found in the Atlantic, while the single male 
of the Siboga plankton was taken in the Pacific. With the exception 
