Boone, Crustacea, Cruises of "Ara" and "Alva" 257 



pace and moderately stout abdomen, as shown in plate 102. The 

 rostrum is extremely short, arising a very short distance behind 

 the orbital margin and extending only as far forward as does the 

 basal antennal article. Viewed dorsally, the rostrum is triangu- 

 late with a median crest, beset with eight teeth ; seen in profile, 

 this crest originates as a low carina on the carapace, not more 

 than two millimeters behind the frontal margin and has its upper 

 border convex, narrowing anteriorly to an acuminate apex; the 

 superior margin is beset with eight short, sharp, serrate spines, 

 the proximal of which is above the carapace, the second, third 

 and fourth spines above the orbit, the remaining four, which are 

 also of successively diminishing size, are spaced along the de- 

 flected distal portion of the rostrum. The interspaces between 

 these dorsal teeth are setose. There are two weak spines on the 

 short, upcurved, subdistal portion of the inferior rostral margin. 



The rostral formulae of the present series of Peruvian speci- 

 mens is as follows: 



Females |, |, |, |. Males: largest |, next |, third |, smallest |. 

 There is a distinct short, stout, acuminate post-orbital spine 

 present, otherwise the carapace is glaucous, as is also the abdo- 

 men, except the telson. The latter is shorter than the uropoda, 

 triangulate, tapered to a narrowed, blunted apex and bears dor- 

 sally two pairs of articulated spines, placed sub-median and sub- 

 distal. 



The first and second basal articles of the inner antennae each 

 bear a small, produced tooth at the outer distal angle ; the flagella 

 consist of three slender, multi-articulate, unequal branches, the 

 longest of which extends not quite to the tip of the dactyl of the 

 lesser great cheliped of the male. 



The outer antennae have the pedunculate article with a spine 

 at the outer distal angle ; the scaphocerite with a subdistal spine 

 at the lateral margin, the distal margin convex, these two arti- 

 cles, considered together, being one-half as long as the carapace ; 

 the flagellum is two-branched, the longer branch extending to 

 midway the dactyl of the greater cheliped of the male. 



The eye is not very large, subspherical, extending only two- 

 thirds of the length of the very short rostrum, the visual range 

 is chiefly lateroventrad. The stalk is expanded dorsally; the 

 cornea is black, convex, composed of quite small facets. 



