PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 429 
The armature of the carapax, chelipeds, and ambulatory legs is more 
like WM. Bamfia than tenuimana. There are usually six subequal and 
nearly equidistant spines upon the anterior half of the lateral wargin of 
the carapax, of which one is in front of the cervical suture, three upon 
the hepatic region, and two upon the anterior part of the branchial 
region. There are no spines upon the posterior border of the carapax 
and none upon the abdomen, except two very small ones on the anterior 
edge of the second somite. The chelipeds are very long and slender, in 
large specimens being a half or more longer than the entire body, 
nearly cylindrical, and the merus and carpus sparsely armed with small 
spines; but the chela, which is longer, but no stouter, than the merus, is 
without spines. 
Four specimens give the following measurements: 
| 
Roce OU a onin ies 
L 
|mm.| mm.) mm ; mm. 
LBP tio penees hotch Gene es SeSEND CBOE CO EROS DOS OD SSEDE AAO B Sep oOuSce SS eeesposaes | 48.2 
5 | 48.0 | 23.0] 17.5 
enc Momeara pax. Nelo dine TOShOM is... 2s 252 siseisecee cere one esse eee se | 25.0 | 24.2 | 12.3 9.2 
Zlienailh ale ROSA 5a, SLE eee ee Oe ee Se eas 6 eee eee tlle eteAGy Th SG) 3.4 
Breadth of carapax in front ince nmicalanGunety. oot sis toa dees eee omnes Waal aber a ean 44 
Greatest breadth, excluding spines. BIBS TAM TEE) 1 OGRA Ihe tae} 
Breadth near posterior margin - i B52) 1253518508! GeO 4.5 
iLosasiin ik hip eGl ABE eae eee ee ea oOo Se eBecOUr re SSopooSrec cho Resr aoe | €4.0 | 79.0 | 86.5) 29.8 
TLictiaiith GP RIGIRIE S220 sadese Secu S eR OC URE BREE See een Cas ACER CaeRoS ar ecaesee | 34.3 | 32.0 | 14.8 8.3 
Length OIRCAT BUS eta oso seats = cee c wesc cece css os cecceeu ws nacesceeces Leek GSO S580) 330 2.0 
Leneth GAP GIGS ROE ee cc ne Se an er een | 39.0 | 36.0 | 15.9 9.8 
Teeieails Ot CCIE) Ghee Sea cect See eee ce Saree te ae ge fein) lg Wa tates 4.3 
Menmihvombnstambulatory logs. o.csce ct saeccasece sence. oeeres one soacee ene POON 477 122, OM g4a0 
Greatest diameter of GYiGis aden boss oOr Bebe oaee See nage Dac DODSaDeEmAEeapecos 4.0} 40 | 3.6 2.0 
| | 
MACRURBA. 
Arctus depressus, sp. nov. 
This species is represented only by a single, small, and probably imma- 
ture individual, but is apparently distinct from any known species of the 
genus, and is readily distinguished by the very broad and greatly 
depressed cephalo-thorax, which in these respects is like Ibacus, and by 
the conspicuous spines each side of the posterior segments of the ster- 
num. The depressed form is perhaps partially a character of imma- 
turity, being an approach to the Phyllosoma-stages, and it is possible 
that the sternal spines disappear in the adult. 
The carapax is less than half as thick as broad, and the breadth is 
much greater than the length along the middle iene above, but slightly 
less than the length of the lateral margin, which is convex in ontline, so 
that the greatest breadth is near the middle of the length. The antero- 
lateral angles are acute and very prominent, extending far forward of 
the rest of the front and to a line slightly in advance of the first dor- 
sally exposed segment (the true second peduncular) of the antenna each 
side. The orbits are very large, almost completely open in front, and 
occupy fully a third of the width of the whole front. The median carina 
is low, being, even in the middle of its length, only a little higher than 
the lateral carinw, and rises into two low, dentiform prominences, one 
