252 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
ECH I NOIDEA. 
SEA-URCHINS, SEA-EGGS, S AND-DOLLARS, SEA-MOONS, ETC. 
The collections made by the Fish Hawk contain over 300 specimens of echinoids, 
but about two -thirds of these represent two species, and half of the remainder are 
supplied by two other common forms. There are 13 species altogether, and all of 
them are well known from the West Indies. Nine of the 13 are distinctly littoral 
forms, but 3 of the others occur only at depths of over 60 fathoms. The remaining 
species, Brissopsis lyrifera , is given by Agassiz (Revision of the Echini, p. 369) as 
occurring at depths of from 55 to 115 fathoms, so that it is worthy of special note 
that the Fish Hawk collected three adult specimens in Mayaguez Harbor in only 7 
fathoms of water. 
The following artificial key will enable anyone to distinguish these species from 
each other, but is liable to prove untrustworthy for young or very small specimens 
and worse than useless where other species are concerned. 
A. Test hard, hemispherical, elliptical, or more or less globular, the height equaling or exceeding 
one-half the diameter. Mouth at center of lower surface. (Sea-urchins proper.) 
I. Test approximately as wide as long. 
a. Spines stout and more or less club-shaped, longer than one-half the diameter of test. 
1. Spines not more than equaling diameter of test Cidaris tribuloidcs. (1) 
2. Spines usually much exceeding diameter of test, often nearly or quite twice as much. Dorocidarls pap illata. (2) 
b. Spines very long and slender (2 or 3 times the diameter of test) with needle-like points... Diadem, a setosum. (4) 
c. Spines short, rather slender and pointed, not nearly equaling diameter of test. 
1. Spines all white or whitish; test brownish or purplish Hipponoe esculenta. (8) 
2. Some of the spines green or greenish, and often with more or less red or violet; test 
usually with a decidedly greenish tinge Taxnpneusi.es variegatus. (7) 
II. Test not as wide as long; usually the difference in the two diameters is very marked. 
a. Apex of test, around anus, covered with numerous small spines Er.hinometra subangularis. (5) 
b. Test about anus almost wholly free from spines EcMnometra viridis. (G) 
B. Test soft and leathery; more or less globular in life; very flat in dead specimens. Deep-water forms. 
(Flexible sea-urchins.) 
I. Color purple above; light yellowish about the mouth Asthengsrma hyslrix. (3) 
(!. Test hard, much flattened, circular or elliptical, the height not one-half of diameter; mouth at center 
of lower surface; spines very short and numerous. (Sand-dollars, key-hole urchins, 
sea-moons, etc.) 
I. Oral surface very concave; test accordingly highly arched Echinanthus msciwns. (9) 
II. Oral surface flat; test not arched, very thin. 
a. Test with six slits (lunules) through it MclKta sexforis. (10) 
b. Test with only five lunules Melltta testudinata.. (11) 
D. Test hard, oval or elliptical; mouth near anterior end on the flattened oral surface; spines 
comparatively short and numerous with or without scattered, long ones. (Spatangoids.) 
I. Size large (over 100 mm.); color deep reddish-purple Palseopneustes hystrix. (13) 
II. Size small (GO mm. or less); color light brown Brissopsis.lyri.fera. (12) 
1. Cidaris trilvuloides (Lamarck). 
This urchin is marbled light brown and white, often with some red, especially on the spines. 
The large spines are comparatively few in number. The test of full-grown specimens is about 60 mm. 
in diameter. This species occurs abundantly in shallow water from South Carolina to Brazil, especially 
about reefs. A large number of specimens were collected at Arroyo and Mayaguez, and at stations 
6075, 6087, and 6096. The largest was 58 mm. in diameter, with spines 45 mm. long. 
2. Dorocidaris papillata (Leske). 
This species resembles the preceding in size and color, but is usually lighter and the spines are 
often almost white; they are also more slender and tapering than in Cidaris. It occurs only in water 
of considerable depth, and is found on both sides of the North Atlantic, from Norway to the Mediter- 
ranean, and throughout the West Indies. Two specimens, one from station 6067, 23 mm. in diameter, 
with spines 53 mm. long, and one from station 6070, 45 mm. in diameter, with spines 83 mm. long. 
