98 BULLETIN 2 01, UNITED STATES NATIONAL MUSEUM 



complicated third pleopod of G. dissimilis. It seems almost impos- 

 sible that Ortmann could have overlooked the extraordinary structure 

 of this appendage if it resembled in any way that which I figure here. 

 Yet the agreement of the two forms is otherwise so close and the 

 geographical localities in which they were found so approximate to 

 one another that I tentatively put forward the suggestion that the two 

 species are synonymous. The matter can be settled only if the type 

 specimen of C. aculeatum is available for examination. If it is not, 

 then Ortmann's name should be canceled as the species is unrecog- 

 nizable. If my suggestion should eventually prove to be correct, then 

 Ortmann's specific name aculeatum will take precedence over dissimilis. 



GASTROSACCUS MEXICANUS, new species 

 FlGUBE 30 



Description. — Carapace produced into a short triangular rostral 

 plate with an obtusely pointed apex, extending about halfway along 

 the eye; a pair of reflected lobes on the dorsal posterior median 

 margin. 



Fifth abdominal somite without a dorsal spine. 



Antennular peduncle wjth two spines on the outer margin of the 

 second joint. 



Antennal scale extending about halfway along the second joint of 

 the antennular peduncle and slightly beyond the distal end of the 

 second joint of its own peduncle, four times as long as broad, terminal 

 lobe slightly overreaching the spine of the outer margin. 



Carpopropodus of the endopod of the third to the eighth thoracic 

 limbs divided into 7 to 9 subjoints, dactylus absent. 



Inner uropod (fig. 30, /) with three spines on the inner margin, 

 one near the statocyst, one near the tip and the third about two-thirds 

 of the distance from the statocyst to the apex. 



Outer uropod (fig. 30, /) with 14 to 16 spines on the outer margin. 



Telson (fig. 30, g) rather long and narrow, about three times as 

 long as broad; lateral margins with from 10 to 12 spines, the distal 

 two of which are much larger than the others and placed quite close 

 together; cleft about one-ninth of the length of the telson with the 

 usual serrated margins. 



First pair of pleopods of the male (fig. 30, a) with the sympod rec- 

 tangular in shape, about twice as long as broad with the usual arma- 

 ture of seven long plumose setae; endopod 1-jointed, shorter than 

 the first joint of the exopod; exopod 4-jointed, the first joint longer 

 than the combined length of the other three. 



Second pair of pleopods of the male (fig. 30, b) with the sympod 

 three and a half times as long as broad and longer than the exopod ; 



