246 BULLETIN 2 01, UNITED STATES NATIONAL MUSEUM 



(2) The rostral plate (fig. 56, a) is shorter and more broadly 

 rounded. 



(3) The antennal scale (fig. 56, a) extends only to the middle of 

 the third joint of the antennular peduncle. In P. orientalis it is 

 slightly longer than the antennular peduncle. 



(4) The cleft of the telson (fig. 56, b) is equal to one-seventh of the 

 total length of the telson. In P. orientalis it is one-quarter. 



(5) There are 18 spines on the lateral margin of the telson, con- 

 fined to the distal three-fifths of the margin. In P. orientalis there 

 are 12 spines occupying the distal five-sixths of the margin. In P. 

 atlantica, therefore, there is a proportionately longer part of the mar- 

 gins of the telson unarmed, and the spines are more numerous and 

 more crowded. 



(6) The endopod of the uropods (fig. 56, b) is at least as long as, 

 even slightly longer than, the exopod. It bears 16 spines on its inner 

 margin, the two distal ones longer than the rest, slightly curved and 

 situated at the apex. In P. orientalis the endopod of the uropods is 

 slightly shorter than the exopod, though the arrangement of the spines 

 is closely similar to that in P. atlantica. 



DOXOMYSIS MICROPS Colosi 



Doxomysis microps Colosi, 1920, p. 249, pi. 20, figs. 9a-f. 



Distribution. — The only known specimens were recorded by Colosi 

 from the Galapagos Islands*. 



MYSIDETES CKASSA Hansen 



Mysidetes crassa Hansen, 1913a, p. 18, pi. 2, figs. 3a-g; pi. 3, figs, la-c; 1921, 

 p. 5. 



Distribution. — Known only from a single immature specimen col- 

 lected at Port Albemarle, Falkland Islands, in 40 meters*. 



ARTHROMYSIS MAGELLANICA (Cunningham) 



Macromysis magellanica Cunningham, 1871, p. 497. 

 Antarctomysis sp. Zimmer, 1915b, p. 170. 

 Arthromysis chierchiae Colosi, 1924, p. 4, figs. 1-3. 



Distribution. — Known only from the Straits of Magellan, from 

 which all the specimens referred to in the synonymy were collected. 



Remarks. — This species was named by Cunningham in 1871 from 

 specimens collected by H. M. S. Nassau in 1867 at the eastern entrance 

 of the Strait of Magellan. Cunningham's description, which was not 

 accompanied by any figures, is very inadequate, and beyond the one 

 positive character, "terminal segment of pleon deeply bilobate," there 

 is no way the species could be recognized. Learning that the Nassau 

 collections were presented to the British Museum, I applied to Dr. 



