172 CRUSTACEA. 



region may be distinguished. In the figure in D'Orbigny's Crustacea 

 of S. America, the margin appears to be reflexed, which is not the fact 

 with the species. The front is two-lobed, with each lobe emarginate 

 or bidentate. The antero-lateral margin consists of ten teeth, the 

 two preceding the last being partly double (or nine, considering the 

 last three as double). The last is the fifth normal (or S). The 

 species is remarkable for the unusual length of the third joint of the 

 outer maxillipeds, the apex being prolonged forward and narrowing. 

 In our specimen a dried, weathered one the first joint of the outer 

 antennae does not reach the front, and is like that of Pseudocarcinus. 



X. Orbignyi, M. EDWARDS and H. LUCAS, D'Orbigny's Crust. S. A., 14, pi. 7, fig. 1. 



SUBGENUS PARAXANTHUS, Lucas. 



If the group Paraxanthus is retained as distinct, the following spe- 

 cies should be referred to it. It has the horizontally-produced front, 

 the rounded and expanded sides, the narrow abdomen, and the short 

 antennary joint of the typical species of Paraxanthus. 



PARAXANTHUS SEXDECIMDENTATUS (Edw. and Lucas), Dana. 

 Callao, Peru, or Valparaiso. 



Length of carapax of a male, one inch five lines; greatest breadth, 

 two inches; ratio of length to breadth, 1 : 1 - 41. The areolets are 

 about as distinct as represented in the figure of Etisus levimanus 

 (PI. 10, fig. 1), and are wholly misrepresented in the figure in D'Or- 

 bigny's work. The nine teeth of either margin of the carapax (eight 

 exclusive of the orbital), correspond normally as follows : the eighth 

 to S ; the seventh and sixth to T ; the fifth and fourth to N ; the 

 third and second to E; and the first or orbital is D. This arrange- 

 ment is apparent, as in other cases, from their position with reference 

 to the areolets 2 L, 3 L, 4 L, adjoining. The ninth tooth is a posterior 

 one (s), and the species thus approximates in form to some Cancers. 



Xantho sexdecimdentatus, M. EDWARDS and H. LUCAS, in Crust., D'Orbigny's S. A., 

 15, pi. 7, f. 2. 



