8t> BULLETIN 60, UNITED STATES NATIONAL MUSEUM. 



Other localities. — Off the eastern coast cf the United States between 

 81) - 53' and 37" 34' 30" north latitude at Alhatrof<s stations 2030, 2171, 

 2179, 21S0, 2181, 2201, 2202, 2215, 2216, 2234, 2235, 2546, 2552, 2680, 

 2691, 2739. 2742, 2744, 2749, in 444 to 963 fathoms, chiefly on carapax 

 of Geryon quiixjvedeus. Fish Commission Station 1140, off Marthas 

 Vineyard, 374 fathoms, on Geryon. Alhatross Station 2237, Hamp- 

 ton Roads. 12 fathoms on Geryon. Off Key West, Florida, 70-80 

 fathoms, on Seyrariiat1iiacra.'<sa^ State University of Iowa Expedition, 

 1893. 



The capituhmi is inequilateral, oblong, the occludent border oidy 

 weakly convex, the carinal strongl}- so. The plates are white or 

 faintly pink-tinted, gloss}^, with minute sculpture of fine radial strife 

 and low rather coarse concentric wrinkles; the narrow area between 

 the occludent margin and the apico-umbonal keel has very fine oblique 

 strias. 



The scutum has a moderately arcuate occludent border, the greatest 

 curvature being near the apex and base. The umbo is somewhat pro- 

 duced and incurved. The basal margin is short and oblique. Onl}" 

 a very weak trace exists of a curved ridge from umbo to the junction 

 of tergum and carina, and there is no distinct angle in the outline of 

 the plate at the tergo-carinal suture. A distinct ridge or angle runs 

 from the um])o to the apex, nearly straight in its apical half, and 

 defining a narrow occludent area. Internally there is a strong but 

 narrow rounded basal rib and a stout but low umbonal tooth. The 

 two scuta are more or less unequal in convexity. 



The tergum is small and wedge-shaped, but wider than the carina, 

 the carinal end being truncate or rounded. It has radiating and 

 growth stria?. 



The carina is regularly arcuate, very narrow and slender, with nar- 

 row rounded roof. The roof is slightly wider above than near the 

 umbo, but the sides are somewhat wider below. Internally the sur- 

 face is concave near the umbonal end, elsewhere convex. There are 

 no distinct teeth, and no post-umbonal expansion or disk. 



The peduncle is short, one-half to one-fourth the length of the capit- 

 ulum, with prominent annuli as in related species. 



Length of the capitulum 11.5, width 7, diameter 3.2 mm. 



The mouth parts and cirri closel}' resemble those of P. kcempferi^ 

 but the edges of the teeth of the njandible are slightly serrate. 



This species ranges along the east coast of the United States from 

 Marthas Vineyard to Key West, usually living on the crab Geryon 

 quinquedens, often in great profusion, in depths of 600 to 800 fathoms, 

 though one lot was taken in but 12 fathoms. It is very variable in the 

 degree of asymmetry, some individuals being nearly symme^^rical 

 bilaterally. Either the right or the left scutum may be the more 



