THE BRACHYURA AND MACRURA OF PORTO RICO. 
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Family PAL^EMONIDTE Leach, iSk). 
Carapace dorsally rounded and laterally compressed; rostrum long, laterally compressed and 
generally armed with teeth. Eyes well developed and pyriform. First antennae with basal joint 
dorsally hollowed, with a strong spine on outer side, and frequently one of the flagella branched; 
second pair with a long and narrow foliaceous scale, its rigid outer margin ending in a small tooth. 
The mandibles have molar tubercle and cutting edge, and either have or have not a palp. Third 
maxillipeds pediform. First two pairs of trunk-legs chelate, the chelce of the second pair generally 
larger than those of first; carpus not subdivided. 
Key to the Porto Rican genera, of the family Palxmonidse. 
A. Carapace with hepati'c spine. 
B. Mandibles with a palp. Body stout. Eyes short and thick Bithynis 
B'. Mandibles without a palp. Body and eyes elongate Urocaris 
A'. Carapace without hepatic spine. Mandibles with a palp Palsemon 
Genus BITHYNIS Philippi. 
Bithynis Philippi, Arch. f. Naturg., xxvi, 1, p. 161, 1860. 
Palsemon Stimpson, Proc. Acad. Nat. Sci. Phila., xii, 41 (110), 1860. 
Carapace with a single lateral spine on front margin, and behind it a second spine, on hepatic 
region. Rostrum clentated. Inner antenme with three flagella. Mandibles with a three-jointed palp. 
First pair of feet slender, second pair much longer and thicker. Species usually fluviatile, often attain- 
ing a large size and with second pair of legs greatly developed. 
Key to the Porto Rican species of the genus Bithynis. 
A. Large chelipeds with palm cylindrical or nearly so. 
B. Chelipeds rough. 
C. Fingers of large chelipeds covered with a thick felt-like coating of stout set* acanthurus 
C'. Fingers naked . jamaicensis 
B'. Chelipeds smooth savignyi 
A'. Large chelipeds with palm swollen and compressed, wider than the carpus olfersii 
Bithynis jamaicensis (Herbst). 
Cancer (Asiacus) jamaicensis Herbst, Natur. Krabben u. Krebse, ii, 57, pi. xxvn, i. 2, 1792. 
Palemon jamaicensis Milne Edwards, Hist. Nat. Crust., ii, 398, 1837. 
Bithynis jamaicensis Pocock, Ann. Mag. Nat. Hist. (6), in, 10, 1889. 
Rostrum about as long as peduncles of inner antennae; teeth, 11 to 14 above and 3 to 5 below; 
upper margin strongly arcuate above eyes. Chelipeds of second pair equal — rough in young indi- 
viduals, but provided with strong spines in the old ones. Carpus considerably shorter than merus, 
thickened in distal portion. Palm subcylindrical, slightly compressed in old specimens, but not 
much thicker than contiguous extremity of carpus; more than three times as long as wide. Fingers 
about as long as palm. Telson rounded at end, on either side two short movable spines. 
Length of body of Porto Rican specimen, 21.5 cm. ; length of second cheliped, 24.5 cm. 
Fresh waters of the Pacific slope, from Lower California to Ecuador; and of the Atlantic slope, 
from Texas to Rio de Janeiro, including the West Indies. Porto Rican localities: Caguas, Rio Grande; 
San Juan market; San Sebastian (A. B. Baker, coll.); Arroyo. 
Bithynis acanthurus (Wiegmann). 
Palsemon acanthurus Wiegmann, Arch. f. Nat., ii, pt. 1, p. 150, 1836. 
Palemon forceps Milne Edwards, Hist. Nat. Crust., ii, 397, 1837. 
Palemon macrobrachion Herklots, Addit. Faun. Afr. Occ., p. 15, 1851. 
Palsemon africanus Kingsley, Bull. Essex Inst., xiv, p. 107, 1882. 
Bithynis acanthurus Rathbun, Proe. U. S. Nat. Mus., xxii, No. 1199, p. 315, 1900. 
Rostrum a little variable, rectilinear or slightly curved upward, as long as or longer than antennal 
scales and longer than stalk of inner antennae; it has 8 to 12 teeth above and 4 to 7 below. Second 
pair of feet almost cylindrical, equally developed, spiny in the old and rough in the young; carpus 
considerably longer than merus; palm cylindrical; fingers shorter or just as long as palm, in the old 
like felt; spines strong, arranged in longitudinal series. Telson short-pointed, inner of side teeth 
overreaching extremity. 
