406 REPORT OF COMMISSIONER OP FISH AND FISHERIES. 



\rith an incomplete, very dense whorl of fine slender hairs; pleon seg- 

 mented, elongated ; palpus of maxillipeds one-jointed. 



The most important character of this genus is doubtless found in the 

 structure of the antennulae in the male sex. In the females the anten- 

 nulsB are small, and the flageUum consists of a few slender rapidly 

 tapering segments. They thus bear considerable resemblance to 

 young specimens of Anthura polita, and being collected with them, 

 were at first mistaken for them. They are distinguished by the larger 

 and more conspicuous eyes, and by the more elongated and distinctly 

 segmented pleon. In the presence of eyes our species differs from a 

 form described by G. O. Sars, Paranthura tenuis, from near Stavanger, 

 Norway, in which the males have a well-developed, eight-jointed and 

 densely hairy or setiferous flagellum on the antennulae. 



PtUanthura tenuis Harger. 



Ptilanthura tenuis Harger, Am. Jour. Sci., Ill, vol. xv, p. 377, 1878; Proc. U.S. 

 Nat. Mus., 1879, vol. ii, p. 162, 1879. 



Plates XI and XII, Figs. 71-74. 



Males of this species are at once recognized by the greatly developed 

 antennulsB, resembling miniature bottle-brushes; females may be dis- 

 tinguished from the young of the other species by the conspicuous eyes; 

 they are much smaller than the adults of the other species. 



The body is smooth, flattened above, narrow at the middle, broadest 

 at the base of the pleon. Head broader than the first thoracic segment 

 and nearly as long, on the median line ; longer than broad, narrowing 

 to a point in front and much less acutely behind. The eyes are j)romi- 

 nent, black, situated within the margin of the head and visible both 

 above and below. The antennulas in the males (pi. XII, fig. 74 a), when 

 reflexed, attain the third- thoracic segment; the first segment is large, 

 but not longer than the second ; the third is shorter than the second 

 and followed by a short, subtriangular segment, which must be regarded 

 as the first segment of the flagellum, although resembling the last 

 peduncular segment much more than it does the succeeding or second 

 flagellar segment ; this segment is small at its base, but expands rapidly 

 above and below and on the side which is next the body in the ordinary 

 reflexed j)osition of the antennula, aud on these sides it bears, at its dis- 

 tal end, a fine and dense fringe of long slender hairs, which attain, when 

 appressed, about the fifth following segment. Similar segments, to the 

 number, in some specimens, of eighteen or twenty follow, forming an 

 organ resembhng a minute bottle brush or plume, whence the generic 

 name. On one side, however, of the organ, which corresponds nearly 

 with tbe outer or anterior side, according as the antennula is more or 

 less reflexed, the whorl of hairs is interrupted. In the females (pi. XI, 

 fig. 73) the antennulae are shorter than the antennae, with a short flagel- 

 lum consisting of a small basal segment and a minute terminal one 

 tipped with a few setae. The antennae {yl. XII, fig. 74 &) are short, 



