30 



distinctly widened, wider than in the middle. In the male of A. scniidciitatiis the inner flagellum 

 reo-ularly tapers, being not broadened and the basal part, that is only slightly bent and twisted, 

 is not concave at the inner side. The scaphocerite, that is not so strongly thickened at the tip 

 as in the male of A. virilis^ appears also, with regard to the length of the carapace, shorter 

 than in that species. In a male of A. virilis which was also captured at Stat. 262, the carapace, 

 rostrum excluded, is 28 mm. long and the scaphocerite, long 21 mm., measures just three- 

 fourths that length; in the male of A. seinidentatus these numbers are respectively 27 mm. 

 and 17,5 mm., the scaphocerite measuring hardly two-thirds the length of the carapace. In 

 the male of A. virilis the external maxillipeds are just as long as the i^' pair of legs, but 

 in the male of A. seinidentatus they extend with the length of the dactylus beyond the extremity 

 of these legs and the penultimate and antepenultimate joints appear in A. virilis a little more 

 slender. In the male of A. semidentattis the i*' pair of legs reach to the end of 2°<i antennular 

 article and the 3''^ to the tip of the antennal scales; the two posterior legs are almost equally 

 long, reaching with their dactyli and one-fourth of the propodi beyond the tip of the scaphocerites. 

 As regards the relative measurements of the merus and the carpus of 3''^ legs, the two species 

 apparently do not differ from one another. In the male of A. virilis the merus and the carpus 

 of 3'''^ legs are respectively 11,5 mm. and 14 mm. long, in the female 12,5 mm. and 16 mm.; 

 in the male of A. semidentattis these numbers are respectively also 11,5 mm. and 14 mm., 

 in the female 13,5 mm. and 16 mm. There are, however, other differences. In the male (not 

 in the female) of A. seinidentatus the lower margin of the merus of the i^' pair of legs appears 

 in the middle slightly concave, but in the male of A. virilis quite straight, and the chelae 

 of the three legs are, in A. seniidentatus, distinctly shorter with regard to the carpus 

 than in A. virilis. In the male of A. virilis from Stat. 262 the carpus of 3''^ legs is 14 mm. 

 long, the chela 12,5 mm. and in the female of the same species these numbers are respectively 

 16 mm. and 14 mm.; in the male o( A. seinidentatus, however, these numbers are respectively 

 14 mm. and 10,5 mm., in the female 16 mm. and 12,5 mm. 



In the female, somewhat larger than the male, the carapace, 33,5 mm. long, is slightly 

 shorter than the rostrum that is 36 mm. long; the rostrum that reaches with half its length 

 beyond the antennular peduncle, e.xtends by one-third of its length beyond the tip of the 

 scaphocerites, and, while the basal portion is slightly directed downward, the slender, and 

 styliform, apical part is distinctly ascending. 



The external maxillipeds that reach to the end of 2'"' antennular article, project with 

 half their dactyli beyond the i^' pair of legs, while the 3"^ legs extend to the distal third of 

 the scaphocerites. The two posterior pairs of legs are subequal and almost reach to the tip 

 of the scaphocerites. 



The pleurobranchia of somite XIII of the female is 2,5 mm. long and bears 19 or 20 

 mostly bi- or trifurcate pinnulae. 



In both specimens body and thoracic aijpendages are glabrous and polished, the fingers 

 are of a pale reddi.sh colour. 



Remarks. This species is very closely related to A. occidentalis Fax. from the 

 Galapagos Islands, but in this form the pleurobranchiae of the somites X — XIII .should bear 



3° 



