40 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.18 



Uropod 3: rami slender, lanceolate, outer more slender than inner; 

 both rami slightly setose. 



Telson moderately slender, apices medially notched, each notch with 

 a stout spine ; dorsal surface of each lobe with 5 stout spines. 



Pleon segment 3: posterior edge nearly straight, lower posterior 

 angle produced into a small tooth. 



Pleon segment 4 slightly raised dorsally, slightly concave, posterior 

 edge rounded. 



Pleon segment 6: lateral ridges slightly developed. 



Description of male: Anterior dorsal portion of head slightly more 

 produced than in female; antenna 1 reaching beyond peduncle of an- 

 tenna 2 ; antenna 2 longer than body, article 3 of peduncle stouter than 

 in female; peduncles of antennae with setal tufts; pleon segment 3, 

 dorsal posterior surface produced into a moderately strong carina ; pleon 

 segment 4 strongly produced ; lateral ridges of pleon segment 6 strong. 

 The third uropods are strikingly different from those of the female and 

 open the question whether this is actually the male of the species as 

 based on the female holotype, although other species, such as A. lobata 

 Holmes, also show this sexual dimorphism. All other characteristics of 

 the male appear to be within the range of variation encountered in the 

 female material. 



Types: Holotype, AHF no. 3913, female, 6 mm; paratypes, 5 fe- 

 males; allotype, male, 5.5 mm. 



Type locality: Station 964-39, Tenacatita Bay, Mexico, 2 to 8 fms. 



Material examined: Stations 122-33 (2), 264-34 (1), 475-35 (266), 

 480-35 (6), 770-38 (1), 964-39 (12), 2026-51 (4). 



Remarks: The length of the fifth article of the peduncle of an- 

 tenna 2 varies considerably. In the holotype and the figured paratype it 

 is longer than article 4 ; in the other specimens it may be subequal to or 

 shorter than article 4. 



In young specimens the head is narrower vertically than in the type 

 material, not as laterally compressed, and the lower pair of eyes may be 

 situated at the lower anterior angle of the head. The range of varia- 

 tion in these characters seems to indicate that they have no specific value. 



This species appears to be closely related to Ampelisca hancocki, new 

 species, but differs essentially in the weak tooth of pleon segment 3 and 

 the relative proportions of the rami and peduncle of uropod 1. 



Distribution: South Bay, Cedros Island, 16 to 19 fms; Tenacatita 

 Bay, and south of White Friars Islands, Mexico, 4 to 25 fms; off San 

 Jose Point, Guatemala, 7 to 11 fms; Salinas Bay, Costa Rica, 12 to 

 20 fms. 



