THE CANCROID CRABS OF AMERICA 169 



Measurements. — Male holotype, length of carapace 66, width of 

 same including spines 77, width without spines 65, length of right 

 cheliped 96, of left cheliped 55 mm. 



Range. — Known only from the unique type, taken off St. Lucia, in 



151 fathoms, temperature 57° F., station 219, U.S.C.S.S. Blake (3054, 



M.C.Z.). 



Genus PLIOSOMA Stimpson 



Pliosoma Stimpson, Ann. Lj^c. Nat. Hist. New York, vol. 7, 1860, p. 227 [99]; 

 type, P. parvifrons Stimpson. 



Body rotund-ovate, longer than wide. Fronto-orbital region very 

 narrow, tumid. Front shallow, rostrum medially fissured. Eyes 

 small, retractile, longitudinally extended. Orbits deep, directed an- 

 teriorly, external angle prominent, upper margin with one fissure. 

 Basal article of antenna just filling the inner hiatus of the orbit; 

 movable part of medium size, excluded from orbit. Epistome very 

 •short, almost obsolete, concealed by the apex of the outer maxillipeds. 

 These last are elongate; distal inner part of ischium produced, merus 

 notched at inner angle; exognath large, narrowing toward the apex, 

 armed inwardly with a tooth. Chelipeds very long in well developed 

 male. Legs slender, first and second pairs cylindrical, first pair much 

 the longer; third and fourth pairs compressed toward the extremity 

 and ciliate; dactylus of last pair almost natatoiy. Sternum anter- 

 iorly veiy broad, narrowdng behind. 



Contains only one species. 



PLIOSOMA PARVIFRONS Stimpson 



Plate 74 



Pliosoma parvifrons Stimpson, Ann. Lye. Nat. Hist. New York, vol. 7, 1860, p. 

 228 [100], pi. 3, fig. 6 (type-locality. Cape St. Lucas; types, Cat. No. 2084, 

 U.S.N. M.; Cat. No. 1242, M.C.Z.).— Rathbun, Bull. Amer. Mus. Nat. 

 Hist., vol. 48, 1923, p. 621, pi. 26; p. 636 (megalops), pi. 36, fig. 2. 



Diagnosis. Carapacelonger than broad. Orbits and eyes directed 

 forward. Chelipeds and first two legs long and slender. Last two 

 legs subnatatory. 



Description. — Carapace convex, pubescent; median regions well 

 separated from the hepatic and branchial ones. Upper surface armed 

 with erect blunt spines, as follows : Four large and seven small ones on 

 the gastric region, the large ones on its posterior part; one on the car- 

 diac, and one on the intestinal region, curved forward; two on the 

 inner part of the branchial, and two longer ones on the anterior part 

 of its lateral margin; two or three small ones on the hepatic region. 

 In the old, well developed individual the dorsal spines are reduced in 

 size, the gastric, hepatic, and two inner branchial prominences being 

 scarcely more than tubercles. There is also a spine on the middle of 

 the pterygostomian ridge. The fronto-orbital region|occupies about 



