THE BRACHYURA AND MACRURA OF PORTO RICO. 
9 
Genus TETRAPLAX, nov. 
Carapace quadrilateral; lateral margins dentate, somewhat converging posteriorly. Front about 
one-third the width of the carapace, margin nearly straight. Orbital margins nearly transverse. Eye- 
stalks elongate and of moderate thickness. Antennae entering the orbit. Buccal cavity wider in front 
than behind. Maxillipeds not completely tilling the cavity; palpus articulating at the front inner 
angle of merus, which is slightly notched. Abdominal segments in male narrower than the sternum; 
third to fifth segments fused. Chelipeds unequal, heavy, angular; fingers pointed. Ambulatory legs 
long, slender, compressed; dactyli of last pair concave upward and outward. 
Type, Frevillea quadrklenlala Rathbun, a species described from the female only. Having 
recently compared the male with the male of F. barbata A. Milne Edwards, I find the species gener- 
ically distinct. Frevillea has very oblique orbital margins, terminating in a prominent antero-lateral 
spine, very stout eyes, while the abdomen of the male is very broad at base, covering the sternum. 
Tetraplax quadridentata Rathbun. 
Frevillea quaclridentala Rathbun, Bull. Labor. Nat. Hist. State Univ. Iowa, iv, p. 287, pi. vin, f. 1, 1898. 
Carapace thick', about three-fourths as long as wide, covered with a short, dark -colored pubescence; 
when this is removed, the regions can be made out. Front about one-third the width of carapace, 
deflexed, edge thin, from above appearing slightly emarginate. Superior margin of orbit sloping 
outward and slightly backward to outer orbital tooth; a notch toward inner end, and another next 
outer tooth. The inferior margin has a notch next the outer tooth and a tooth at inner angle, between 
which and the antenna there is a triangular opening. Antero-lateral margin with three teeth besides 
the orbital; their outer edges are finely denticulate; the three teeth are very nearly in a line parallel 
to middle line of crab; orl >ital tooth less pr< ijecting. Postero-lateral margins longer than antero-lateral, 
and moderately converging. The sutures between the third and fourth, and fourth and fifth segments 
of abdomen of male are partially indicated. Terminal segment rounded at extremity. Chelipeds 
subequal, rather heavy. Merus with a spine on its superior margin at its distal third. Carpus with 
an inner spine and an anterior fringe of hair. Hand smooth and shining, finely granulate above, upper 
margin acute and very finely granulate. Lower outer margin of pollex with a granulated costa. 
Dactylus with two superior granulated coshe and a superior fringe of hair. 
The dimensions of three specimens from San Juan Harbor are as follows: 
Sex. 
Length. 
Width. 
Width 
at antero- 
lateral 
angles. 
Width 
of front. 
Male 
8.3 
10.3 
9 
3.5 
Ovigerous female 
8.1 
10.4 
9.1 
3.6 
Male 
5.8 
6.8 
6.4 
2.5 
San Juan Harbor, 4b to 5£ fathoms, sand, mud, station 6054, 2 males, 1 female; Mayaguez Harbor, 
12 fathoms, sticky mud, station 6060, 1 male. One specimen only, a female, had been taken previously 
by the Albatross at Curasao. Three of the Porto Rican specimens are larger than the type and show 
that the species becomes relatively narrower as it increases in size. 
Genus CHASMOCARCINUS Rathbun. 
CAksmocarcinus Rathbun, Bull. Lab. Nat. Hist. State Univ. Towa, iv, 284, 1898. 
Carapace thick, broadest posteriorly, tapering anteriorly, without antero-lateral angles, the lateral 
margins forming a curve continuous with the anterior margin. Front narrow, bifid. Orbits marginal, 
oblong; eyes movable. Pterygostomian region with a horizontal suture as in Scalopidia. Antennula 
with basal joint very large and hemispherical. Epistome nearly perpendicular, its margin projecting 
below the maxillipeds. Maxillipeds widely separated throughout their length, longitudinally placed. 
Merus suboval, the palpus articulating at the antero-internal angle. Abdomen much narrower at base 
than the sternum; third, fourth, and fifth segments coalesced in the male. The sexual appendages 
pass to the coxfe through ducts visible between the sternal segments. Abdominal segments distinct in 
the female. Chelipeds with merus trigonal, carpus quadrate, manus short and broad, fingers long and 
slender. Ambulatory legs slender, subcylindrical, the third pair the longest, the second next, the 
fourth the shortest. Dactylus of last pair recurved. 
