20 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.18 



In very large specimens of this species (16 mm, from Stations 576- 

 36 and 704-37), the lower posterior corner of pleon segment 3 is very 

 minutely produced. This same phenomonon is also exhibited in large 

 specimens of Ampelisca lobata Holmes. 



Distribution : Along the coast of southern California and in the Chan- 

 nel Islands, 15 to 275 fms; Gulf of California at Angel de la Guardia 

 Island, Isla Partida, Angeles Bay, San Marcos Island, Tortuga Island, 

 and Tiburon Island, 8 to 70 fms; Isabel Island, Mexico, 10 to 25 fms; 

 Salinas Bay, Costa Rica, 1.5 to 6 fms; Secas Islands, Panama, 12 fms; 

 Santa Elena Bay, Ecuador, 8 to 10 fms. 



Ampelisca isocornea, new species 

 Plate 12 



Description of male: Head not quite as long as first 3 body segments, 

 anterior edge broadly incised, lower front edge oblique, concave. Upper 

 pair of eyes suboval in outline, equal in size to lower pair of eyes ; lower 

 pair on lower front edge of head below lateral angle. 



Antenna 1 reaching beyond the peduncle of antenna 2; peduncle 

 stout; article 2 about one and one-half times as long as article 1, article 3 

 shorter than 1. 



Antenna 2 longer than body; article 5 of peduncle seven eighths as 

 long as 4. 



Mandible: spine row with 10 spines; palp article 3 two thirds as 

 long as article 2. 



Maxilla 1: outer plate with 10 spines; palp article 2 about as wide 

 as outer plate, apex with 4 spines, 3 cusp teeth, and 11 or 12 setae. 



Maxilliped: apex of inner plate with 2 chisel teeth; inner edge of 

 outer plate with 8 chisel teeth; rounded apex with 7 setal spines, the 

 outer 4 of which are plumose. Palp normal. 



Gnathopod 1 : article 6 almost as long as 5, posterior edge slightly 

 convex ; article 7 large, about two thirds as long as article 6. 



Gnathopod 2 very slender; article 6 more than one half as long as 5 ; 

 article 7 slightly more than one half as long as article 6. 



Coxal plates 1 to 3 : lower posterior angle with a small slit. 



Peraeopod 1 rather stout ; distal ends of article 4 very slightly pro- 

 duced ; article 7 longer than 5 and 6 combined. 



Peraeopod 2 very stout, very strongly setose. 



Peraeopod 3 : anterior edge of article 2 setose ; article 6 shorter than 

 5, posterior edge with 2 spines; posterior edge of article 5 with 3 sets of 

 spines. 



