A REVIEW OF THE MYSIDACEA 89 



setae on the outer margin; endopod small and 1-jointed; exopod 5- 



jointed. 



Second pleopod of the male (fig. 24, c) similar to the first but with- 

 out plumose setae on the outer margin of the peduncle, the outer 

 ramus 6-jointed. 



Third pleopod of the male (fig. 24, d) (in an immature specimen) 

 with a short peduncle; endopod single-jointed; exopod greatly de- 

 veloped and divided at the distal end into two digitate lobes. 



Fourth and fifth pleopods (figs. 24, e-f) of the male similar; rami 

 slightly longer than the peduncle; endopod single- jointed; exopod 

 slightly longer than the endopod and 3-jointed. 



Occurrence. — La Jolla, Calif., Scripps Institution : Haul 137, Sep- 

 tember 13, 1916, 1 specimen; Haul 1720, April 26, 1917, 1 specimen; 

 Haul 1966, June 16, 1917, 2 specimens ; Haul 3005, January 8, 1918, 

 2 specimens. 



Distribution. — Known only from California (Holmes and 

 Tattersall). 



Remarks. — Having examined specimens that I believe represent the 

 true Archaeomysis grebnitzhii it is now possible to state that the speci- 

 mens which I recorded in 1932 as A. maculata are in reality very dis- 

 tinct from A. grebnitzhii and may be separated by the following char- 

 acters : (1) The rostral projection is long and acutely pointed, extend- 

 ing in front beyond the eye; (2) there is a prominent spine on the 

 dorsal posterior margin of the fifth abdominal somite; (3) there are 

 12 spines on the telson whereas in A. grebnitzhii there are only 8; 

 (4) there are 22 spines on the outer uropod whereas in A. grebnitzhii 

 there are only 13. 



Genus GASTROSACCUS Norman 



Oastrosaccus Norman, 1868, p. 438. 

 Acanthocaris Sim, 1872, p. 185. 

 Haplostylus Kossmann, 18S0, p. 94. 

 Pontomysis Czerniavsky, 1882a, pp. 61, 70, 77. 

 Chlamydopleon Ortmann, 1893, p. 25. 



This genus is represented in the United States National Museum 

 by several species, but only three are found in American waters — 

 Gastrosaccus johnso?ii, G. dissimilis, and the new species, G. mexi- 

 canus. All three are characterized by the curious and greatly modified 

 third pleopod of the male but they may be separated by the following 

 characters : G. johnsoni has no reflected lobes on the carapace and no 

 spine on the fifth abdominal somite; G. dissimilis has no reflected 

 lobes on the carapace but it has a prominent spine on the fifth abdomi- 

 nal somite ; G. mexicanus has reflected lobes on the carapace but no 

 spine on the fifth abdominal somite. 



