CANCROIDEA. 295 



The buccal area is well closed by the outer maxillipeds, as is usual in 

 the Cancridae, the orbit is not open on the outer inferior side as in 

 Atelecyclus, the abdomen (narrow in the males, broad in the females), 

 is that of the Cancridse, and excepting the form and the absence of 

 the moveable part of the outer antennae, we should at once recognise 

 them as pertaining to that group. The buccal area is a little nar- 

 rower anteriorly, but this is not sufficient (as it is not connected with 

 an adaptation of the inner branch of the first maxillipeds to the for- 

 mation of a tube for the efferent canal), to prove any relation to the 

 true Oxystomes. Acanthocyclus has the inner antennae unfolding 

 from a longitudinal fissure in the front margin, as in Plagusia; and 

 the form, appearance, and habit, are much as in the thicker Plagusiae. 

 The articulation of the fourth joint of the outer maxillipeds with the 

 inner apex of the third, is also a characteristic of Plagusia. But the 

 narrow sternum behind, and the position of the male verges, exclude 

 the species from any intimate relation with that group; still it exem- 

 plifies, not only a passage from the Cancridge to Atelecyclus, but also 

 to Plagusiae. 



In Acantliocyclus, the front margin of the prselabial area is rather 

 narrow, and has two deep emarginations (somewhat as in Eriphia) as 

 the aperture of the efferent canal, but the palate is without ridges. 



The only known genus referable to this group is Acanthocyclus. 

 Cymo has the same orbicular outline, but has the outer antennae com- 

 plete. The number of branchiae forming the exterior of the branchial 

 pyramid in Acanthocyclus, is but five, and in this respect also, the 

 species approach the Plagusiae, 



ACANTHOCYCLUS GAYI, Lucas. 



Plate 18, fig. 4 a, outer or third maxilliped, enlarged; b, second 

 maxilliped; c, part of first maxilliped. 



Valparaiso, Chili. 



Length of the carapax of a male, nine and three-fourths lines; 

 breadth, ten lines. The carapax is pubescent, especially towards the 

 front and antero-lateral margins. The male abdomen is very nearly 

 naked, though in parts very short tomentose. The under surface of 



