ART. 18 NEW AMPHIPODS FEOM CALIFORNIA SHOEMAKEE O 



corners produced into prominent up-turned processes which are ser- 

 rate on their lower margins. Uropod 1 extending farther back than 

 2 or 3, which are subequal in length. Outer ramus of all uropods the 

 shorter. Telson a little longer than wide, slightly excavate, and 

 having the lateral corners somewhat produced. 



Length. — 4.5 mm. 



Type.—Q^t. No. 63281 U.S.N.M., off Moss Landing, Pacific Grove, 

 Monterey Bay, Calif., taken from rock from 50+ fathoms, collected 

 by the Pacific Biological Laboratories, No. 78.1. 



EURYSTHEUS TENUICORNIS (Holmes) 



Figures 3-4 



1904 Gammaropsis tenuicornis Holmes, Harriman Alaska Expedition: 

 Amphipod Crustaceans of tbe Expedition, p. 239, fig. 124. 



1916 Podoceropsis concava Shoemakee, Proc. Biol. Soc. Washington, vol. 

 29, p. 159. 



This species was described by Prof. S. J. Holmes from a single 

 immature male specimen from Puget Sound. In 1916 I described 

 a species, Podoceropsis concava, from Venice, Southern California. 

 These specimens also were immature, and lacked the antennae. 

 Recently while studying collections from various California local- 

 ities, containing specimens in all stages of development, I found 

 that old individuals differed greatly from the younger ones in cer- 

 tain characters, and that some individuals exhibited the characters 

 of Eurystheus tenuicornis (Holmes), while others possessed those of 

 Podoceropsis ooncaca Shoemaker. There can be no doubt, there- 

 fore, that E. tenuicornis and P. concava are but variations of the 

 same species. 



In the younger males the palm of gnathopod 2 is defined by two 

 low teeth, and the sixth joint is very much longer than the fifth. 

 In males of more advanced growth the palm is defined by a single 

 low tooth, and the sixth joint is very little longer than the fifth. In 

 the oldest males the defining tooth of the palm is much more 

 strongly developed, and the central tooth is distinct from the palm 

 and not a mere triangular projection as in younger specimens, while 

 the sixth joint is considerably shorter than the fifth. Gnathopod 

 2 of the female with palm evenly convex, without defining angle, 

 but possessing two defining spines and having the sixth joint very 

 slightly longer than the fifth. The side-plate of peraeopod 5 in the 

 younger males is of normal proportions, but increases very markedly 

 in size with advancing age until in the old males it attains enormous 

 development and completely covers the second joint of the peraeopod. 

 Pleon segments 2 and 3 with lateral margins strongly convex, and 

 postero-lateral corners indicated by a shallow angle. Pleon seg- 

 ment 4 bears dorsally a backward-pointing tooth and seta on either 



