572 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.51. 



size and shape. Maxillipeds consisting of two broad basal articles 

 obliquely articulated and a minute distal article. Antennae minute, 

 composed of two short articles and completely concealed beneath the 

 margin of the head. Pleopods, four pairs of small, rather broad, bi- 

 lobed plates, growing smaller posteriorly, the last two or three always 

 rudimentary. Uropods wanting. 



Male. — ^About one-fourth as long as the female, symmetrical, about 

 four times as long as wide. Head consolidated with the first thoracic 

 segment, emarginate in front and with a deep notch on each side in a 

 line with the small, black eyes. Thoracic segments rather loosely 

 articulated, their outer ends rounded. Abdomen consisting of five 

 distinct segments, the first thi-ee large, but diminishing in size back- 

 ward, the fourth very small and completely immersed in the third, the 

 fifth a small rounded lobe. Antennae composed of two articles. 

 Pleopods and uropods wanting. Color white or yellowish, usually 

 with a minute pigment fleck on each side of some of the thoracic 

 segments. 



A series of over 20 specimens of this species was secured from the 

 same lot of shrimps as supplied the specimens of Phryxus suhcaudalis. 

 Tliis parasite lives in the giU chamber, either the right or the left, with 

 its dorsal surface resting against the gills of its host. A male is inva- 

 riably found attached to the pleopods of the female close behind the 

 marsupial chamber. 



Among the specimens examined only one female was found with 

 two pairs of well-developed pleopods. The usual condition was to 

 have the first pair obscurely biramous, the next pair rather deeply 

 notched, and the last two pairs much smaller and subquadrate. One 

 male was found which was considerably broader in proportion to its 

 length than the others, owing to the reduction of its abdomen to only 

 three segments. It was clinging to a perfectly normal female. 



PSEUDIONE UPOGEBIAE, new species. 



Plate 100, figs. 7 to 12. 



Holotype. — Cat. No. 48369, U.S.N.M. (female), and paratype from 

 Beaufort, North Carolina, on Upogebia affinis (Say). Collector, W. P. 

 Hay, August 17, 1915. 



Female (holotype). — Body somewhat asymmetrical, longer than 

 broad, irregularly ovate. Head small, deeply immersed in the 

 thorax, with a frontal border the anterior margin of which is sinuately 

 curved and indistinctly cleft in the center. Antennules of three and 

 antennae of four articles the last two of which, in each case, project 

 beyond the frontal border. Thorax with all the segments distract. 

 Ovarian bosses present on the first four segments. Epimera of first 

 four segments reduced to narrow ridges external to the ovarian 



