38 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Genus PILUMNUS Leach. 
Pilumnus Leach, Trans. Linn. Soc. London, xi, 309 and 321, 1815. 
Carapace and legs generally thickly covered with hair. Carapace transversely oval or subquad- 
rilateral, declivous anteriorly, flat posteriorly, not greatly broader than long; the regions, as a rule, but 
moderately plainly demarcated and areolated. Antero-lateral borders not longer, but commonly 
shorter than postero-lateral, and cut into teeth which, very commonly, are spiniform. Front usually 
about a third the greatest breadth of carapace, but sometimes broader. It is cut into two lobes, the 
outer angle of each of which commonly forms an independent dentiform or spiniform lobule separated 
from supra-orbital angle by a groove or notch. The orbits generally have a gap or fissure just below 
outer angle, and one or two gaps or notches in upper border; inner lower orbital angle commonly 
sharp and prominent. Eyes moderately long and slender. The antennules fold transversely. Basal 
antennal joint short, either not quite touching the front or just touching it by its inner angle; the 
flagellum, which is planted in the orbital hiatus, is long, usually very much more than major diameter 
of orbit. Ridges of endostome, defining expiratory channels, are usually plain, but not very high; 
anterior border of merus of external maxillipeds almost transverse and not notched. Chelipeds stout, 
the lingers coarse, short, and pointed. Legs usually stout and of moderate length. The abdomen of 
male consists of seven separate segments. 
Key to the Porto Rican species of the genus Pilumnus. 
A. Carapace for the most part concealed by a short, thick pubescence, which when removed discloses tubercles 
on the hepatic regions and, usually, on the gastric also. 
B. Frontal lobes concave, entire reticulatus 
B'. Frontal lobes convex, and granulate or denticulate. 
C. Outer surface of palms more or less hairy. 
D. Entire outer surface of palms tuberculate gemmatus 
D'. Outer surface of palms partially smooth and naked. 
E. Antero-lateral projections, after the pubescence is removed, spiniform, curved, sharp pannosus 
E'. Antero-lateral projections, after the pubescence is removed, dentiform, short, obtuse holosericus 
C. Outer surface of palms wholly naked or free from hair nudimanus 
A'. Carapace, when covered by a short, thick pubescence, not having the gastric region tuberculate. 
B. Outer surface of larger hand only partially covered with tubercles or spines. 
C. Carapace covered with hair floridanus 
C'. Carapace naked on posterior half dasypodus 
B'. Outer surface of larger hand entirely covered with tubercles or spines. 
C. Four lateral spines, including the orbital brasiliensis 
C'. Three lateral spines, the orbital missing marslti 
Pilumnus reticulatus Stimpson. 
Pilumnus reticulatus Stimpson, Ann. Lyc. Nat. Hist. N. Y., vn, 214, 1860. 
Pilumnus tessellatus A. Milne Edwards, Crust. BOg. Mex., 295, pi. LI, f. 2, 1880. 
Carapace, upper surface of chelipeds, and also the legs clothed with short, thick setae, closely 
arranged in reticulating lines, inclosing small, naked, polygonal areola', which on anterior half of 
carapace and on chelipeds are mostly each occupied by a tubercle projecting forward, but flattened on 
its superior and posterior surface. About twelve tubercles on carapace, excluding marginal ones, and 
fifteen or more on each cheliped. On the legs the naked areoke form deep cavities not occupied by 
tubercles; about two areolte occupy width of leg. Some much longer and larger clavate setse are 
dispersed among the short ones which clothe the general surface. Margins of frontal lobes oblique and 
concave. Antero-lateral margin with four teeth (including the orbital) similar to the tubercles; there is 
also a subhepatic and a subbranchial tubercle. Three projecting teeth on lower margin of orbit, the 
inner one very large. Lower and distal two-thirds of outer surface of larger palm and half of smaller 
palm smooth and naked. Fingers also smooth; only a few setae at base of dactylus. 
Length of male, 8 mm.; width, 11 mm. 
Jamaica; St. Thomas; Curasao; Desterro and Pernambuco, Brazil (A. Milne Edwards). Porto 
Rico: Mayaguez; Playa de Ponce Reef; Arroyo; Puerto Real. 
Pilumnus gemmatus Stimpson. 
Pilumnus gemmatus Stimpson, Ann. Lyc. Nat,. Hist. N. Y., vn, 214, 1860. (Not P. gemmatus A. Milne Edwards.) 
Carapace rather narrow, covered, as also are the chelipeds and legs, with a short, close pubescence 
(with occasional stout and long cylindrical setse), which does not conceal boundaries of regions and 
