THE ECHINODERMS OF PORTO RICO. 
241 
c 2. Upper arm-plates without supplementary plates. 
i. Arm-spines long, glassy, numerous (8); size large (disk over 10 mm. in diameter); 
color dark brown Ophialcrea glabra. (43) 
U. Arm-spines rather short, not glassy, numerous; size medium; color various, but. 
disk usually speckled; scales very minute. 
k. Disk reddish or gray, spotted with black; arm-spines 6 to 7 Ophiopsila rilsei. (23) 
kk. Disk grayish, spotted with orange; arm-spines 6 to 11 Ophiopsila fulva. (22) 
in. Arm-spines short, 3 to 7; size small; arms long; color of disk grayish, arms very 
light; scales very distinct. 
l. Oral papillae 2, one on each side at base of jaw and 1 at the tip; middle of jaw 
edge bare; arm-spines 4 or more. 
to. Tentacle-scale 1; radial shields twice as long as broad; 4 to 5 short, blunt 
arm-spines A mphiura slimpsoui. ( 2.8 ) 
toot. Tentacle-scales 2; radial shields three times as long as broad: 6 tapering 
arm-spines , imphiura flcxuosa. (27) 
nnnm. Tentacle-scales 2, at base of arm ; radial shields twice as long as broad; 6 to 
7 short arm-spines, 2 next to the lowest with little hooks on the end. 
Aviphmra bihamuld. (29) 
U. Oral papillae 3 on each side, the distal one very wide; arm-spines 3. 
n. Arms very long and slender, more than 8 times diameter of disc Amphipholis gocsii. (30) 
nn. Arms less than 8 times diameter of disk. 
o. Radial shields short and joined Amphipholis limbata. (31) 
oo. Radial shields long and narrow Amphipholis subtilis. (32) 
Ul. Oral papillae 3 or 4, subequal or the distal one smallest; arm-spines 3, rarely 4. 
p. Tentacle-scale 1 Amphiodia pulchella. (34) 
pp. Tentacle-scales 2. 
r. Oral shield elongate; arm-spines more or less acute Amphiodia nisei. (35) 
it. Oral shield ovate, broadest proximally; arm-spines flat and wide at tipi. 
Amphiodia planispina. (33) 
till. Oral papillae 5, unequal ; radial shields widely separated; arm-spines 3. 
Amphioplus steams ii. (3(1) 
c 3. Upper arm-plates altogether wanting or consisting of a number of small indistinct pieces. 
s. Upper-arm plates wanting; size small, disk 5 to (1 mm. in diameter. 
Ophioscol<:£ serraias. (46) 
ss. Upper-arm plates indistinct, of several pieces on each side; size large, 
disk 15 to 25 mm. in diameter Opliiomyxa Jtaccida. (47) 
B. Anns slender , capable of being vcrliealli y coiled.; disk very small, not sharply set of from arms. 
I. Color yellowish-brown: arms covered by a granulated skin Ast msehema oHyarles. (49) 
II. Color brown and white; arms ringed by regular raised belts of close-set nodules I stroporpa amvulala. (48) 
The user of this key must be cautioned that it is of no value except for the species 
included. Moreover, in the case of large genera like Opluogl ypha, Ojjh/ormcsmjn, 
Ampliiura , and Ojjhiacantlia, several species might answer to the very brief descrip- 
tions given to the Porto Rican forms, though the attempt has been made to have these 
descriptions reasonably exclusive. It is believed, however, that the ordinary littoral 
forms can be easily and accurately determined by means of this key. The charac- 
ters show much more plainly in dry specimens than in fresh or alcoholic material, 
and this is particularly true of the covering of the disk and the upper and under 
arm-plates. 
2d— r. C. B. 1900— 16 
