THE GRAPSOID CEABS OF AMEEICA. 189 



second tooth a small tubercle or rudimentary tooth. Above posterior 

 margin a thin, sinuous, elevated ridge, broken into a variable number 

 of unequal transverse tubercles, with usually some granules inter- 

 spersed. Suborbital margin oblique, its outer lobe nearly straight 

 and separated from inner lobe by a small emargination ; inner lobe 

 bilobed, its inner angle produced in a small acute tooth beyond the 

 triangular, pter3'^gostomian lobe. 



There are two forms of the male. In the first or stronger, the 

 chelipeds are very unequal, the right large and heavy, the left slender 

 and weak; both are tuberculate and pubescent, the carpus has an outer 

 laminate crest, its outer surface covered with irregular laminiform 

 lobes, manus surmounted by a double crest of same ; right manus very 

 thick, its width at distal end may equal one-half length of carapace, 

 immovable finger short and wide, dactylus strongly bent down, over- 

 lapping the fixed finger and leaving a narrow gape; left manus 

 little over one-third width of right, fingers long and narrow. In 

 the second or weaker form of male, the right manus is about twice 

 depth of left, its fingers long and slender. In the female the 

 chelipeds are more nearly equal. 



Of the ambulatory legs, the first reaches middle of propodus of 

 second, third reaches middle of dactylus of second; merus joints 

 rough, with squamose tubercles, a longitudinal groove on anterior 

 edge, two of same on upper surface, an obtuse tooth at distal end, 

 which in the first leg is subtriangular and produced a little distally 

 beyond segment, in second and third legs is subrectangular, either 

 straight or a little convex above and reaching in second leg just to, 

 or not quite to end of segment, and in third leg not reaching end of 

 segment; anterior proximal lobe of carpus rounded, somewhat tri- 

 angular, anterior subdistal lobe low and rounded on first leg, tri- 

 angular in second and third legs, posterior distal tooth inconspicu- 

 ous; anterior margin of propodus convex, posterior straight; poste- 

 rior margin of propodus and proximal half of dactylus of first leg 

 clothed with shagg}^ hair in adult male. 



In the first form of the male the appendages of the first abdominal 

 segment are stout and twisted, tip bilobed, inner lobe thinner and 

 longer than outer; in the second form the appendages are weaker 

 and not twisted, tip less spreading. 



Except for the chelipeds and abdominal appendages the two forms 

 of the male agree. They may represent alternating generations, as 

 in the crayfish of the genus GaTribarus^ or the weaker specimens may 

 be simply immature. 



Variety. — The species shows such great divergence from type that 

 it seems almost possible to form a second species based on {a) the 

 carapace being wider behind in proportion to its length, 1.15-1.24:1, 

 instead of 1.09-1.21 : 1 in typical altemata^ and the sides less parallel 



