THE GEAPSOID CRABS OF AMEEICA. 67 



forming a rounded lobe, visible from before. Orbits small, sub- 

 circular, anteriorly placed. 



Antennules large, antennae small; flagellum not as long as di- 

 ameter of orbit. Carpus or first segment of palp of outer maxilli- 

 ped, short, oblong; propodus elongate, end rounded; dactyl inserted 

 behind middle of propodus, minute, and very slender. 



Chelae moderate, merus and carpus rather slender; palm flat- 

 tish inside, swollen outside, strongly widened from the proximal 

 toward the distal end, then somewhat narrowed, the width across 

 base of fingers considerably less than greatest width of palm, lower 

 margin of propodus, as well as upper, convex; fingers, especially 

 the immovable one, stout, not gaping, tips hooked past each other, 

 several small teeth on prehensile edges; fixed finger horizontal. 



Legs slender, subcylindrical, last 2 joints with thin fringe of hair: 

 first leg stoutest, propodus widening distally, dactylus about half 

 as long, curved; last 3 legs similar to one another, dactyli longer 

 and straighter; second leg long- 

 est, third next, first and fourth 

 subequal. 



Mature abdomen very large, ex- 

 tending beyond carapace in all 

 directions. 



Description of male. Kela- 

 tively narrower and less swollen 



than female; front more ad- FIG. SO. PINNOTHERES OSTUEUM, OUTER 



vanced, truncate. Chelipeds simi- "^ * -""" (2542), x i5j. 

 lar to those of female but palm shorter, more swollen. First leg as in 

 female, except for the dactylus which is longer, two-thirds as long as 

 propodus, and more curved than in female ; in the remaining legs the 

 carpus-propodus is wide as in the first leg, not slender as in female, 

 and the dactyli are longer than in female, the fourth one quite as 

 long as propodus; they are nearly straight proximally but toward 

 the end are falcate. Sides of abdomen nearly straight and con- 

 vergent from the third to the seventh segment, which is arcuate at 

 the extremity. 



Color. Female. Translucent whitish generally. Upper surface 

 of carapace and median region of post-abdomen red to pinkish. 

 Minute eyes brownish. All limbs whitish (Fowler). 



Measurements. Female (2542), length of carapace 12, width of 

 same 15 mm. Male (49209), length of carapace 1.3, width of same 

 1.4 mm. 



Habitat. Commensal with oysters. Males free-swimming. 



On the coast of the Carolinas P. ostreum is abundant, according to 

 Dr. Bashf ord Dean ; * however, not more than one female was noted 



. TJ. S. Fish Comm., vol. 10 for 1890 (1892), p. 351. 



