G PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



third pair; tlie second pair falling short of the articulation of the rami 

 of the third pair, and terminating about opposite the articulation of the 

 rami of the first i)air. Tel sou minute, uuguiform. 



Male. — The fifth pair of thoracic legs relatively shorter in the male; 

 all the joints of the leg individually shorter and stouter than the corre- 

 sponding parts in the female. The produced portion of the fourth joint, 

 corresponding with the immovable finger of a crab, more produced 

 downward, and less anteriorly, and arises from about the middle of the 

 inferior surface. The fifth joint is more curved at its proximal extrem- 

 ity, so as to antagonize with the produced portion of the fourth joint. 

 These sexual characters of the fifth pair of legs are only developed in 

 the mature male; in the young of this sex, the fifth pair partakes of the 

 characters, more or less, of the young female. 



There were examined twenty-eight specimens of this species, coming 

 from many different localities in the Pacific Ocean, varying in length 

 from 4 to 21""", and there was found no material variation in the struc- 

 tural character of the prehensile organ, dependent upon age (presuming 

 the size of the specimen to be dependent upon its age) ; that of 4"'™, as 

 well as that of 21'""\ presenting all the essential characteristics of the 

 si)ecies as described and figured by Gueriu. The shape of the hand 



as deep posteriorly as anteriorly, and all the joints are relatively shorter 

 and stouter. As the animal increases in size the parts become length- 

 ened, and the hand is much narrower posteriorly than anteriorly. In 

 one specimen only, did the teeth on the anterior surface of the hand 

 show any variation; in that, the detached tooth, nearest the produced 

 portion, was wanting. P. custos, probably, represents this occasional 

 variation. In another example, the prominence on the concave surface 

 of the movable finger was very prominent, almost tooth-like. With these 

 exceptions, I fonnd no tendency to variation in these parts, which is 

 contrary to the researches of Claus. According to this authority, P. 

 atlantica is nothing more than the immature female form of P. sedentaria. 

 I think, however, that the A^alidity of the species will no longer be ques- 

 tioned, now that the male form of P. atlantica is presented. 



Locality (of those examined): Pacific Ocean, north and south of the 

 equator, from latitude 30° 42' south to 37° north; and from longitude 

 81° 40' west to 1()0^ 25' west. The temperature of the water varied 

 from GOO to 79° Fahr. 



Phronima pacific a, Streets. 



(Plate I, Fif?. 3, 3a.) 

 Phronima sedentaria, Claus, Zeitschiift wissen. Zoologie, Leipzig, 1872, XXII, pis. 



xxvi, xxvii, fig. 1-12. 

 Phronima padfica, Streets, Bulletin of the National Museum, No. 7, Wasbiugtou, 1877, 

 p. 128. 

 Female. — The first and second joints of the superior antenuie short 

 (the first narrow, the second broad) ; the last joint about twice the length 



