THE ECHINODERMS OF PORTO RICO. 
255 
Besides the foregoing thirteen species, several other common West Indian eehi- 
noids may be expected to occur along the shores of Porto Rico. These are Clypeaster 
svbdepressus (Gray), Encope emarginata (Gmelin), Encope michelini Agassiz, Echi- 
non&us semilunaris (Gmelin), Brissus unicolor Klein, Meoma ventricosa (Lamarck), 
Metalia pectoralis (Lamarck), and Moira at/ropos (Lamarck). The first four will fall 
under the heading C in the key on page 252, the last four under the heading D. Clype- 
aster resembles Echvncmthus , but may be easily distinguished by its larger, much 
flatter test. It occurs from South Carolina to Brazil and eastward across the Atlantic. 
The two Encopes resemble Mellita , but are larger (up to 140 mm. in diameter), and 
the lunules are different. Those in the radii differ from the one in the posterior 
interradius and are inclined to be elliptical or even oval. The two species of Encope 
may be distinguished from each other by the fact that in emarginata the posterior 
lunule is longer than any of the others, while in michelini it is generally smaller 
than the others. In the latter species, moreover, the anterior lunules often disappear 
with the growth of the animal, so that the test has only one or three lunules left. 
Encope emarginata occurs from South Carolina to Brazil, while michelini is found 
throughout the Gulf of Mexico. 
Echino-neus is quite different from any of the others. Although properly a 
spatangoid, the mouth is central, so that in the key on p. 252 it would come under 
C rather than D. The test is a somewhat flattened ellipse, from 15 to 40 mm. long, 
covered with short, light-brown spines, and with the bright-red feet (in living animal) 
arranged in five double rows, radiating from the center of the aboral side. It lives 
in the sand in shallow water, often under stones, and occurs throughout the West 
Indies. It has been recorded in the past from Porto Rico. 
Brissus unicolor resembles Brissopsis lyrifera , but may be distinguished from 
that species by the position of the center of the ambulacral system. In Brissopsis 
this point is near the center of the test; in Brissus it is far forward. Moreover, 
Brissopsis is a deep-water form occurring only occasionally in a few fathoms, while 
Brissus is found in very shallow water, in the sand, often under stones, in company 
with Echinoneus. Brissus has a wide distribution, being found all through the West 
Indies and eastward across the Atlantic into the Mediterranean. 
Meoma and Metalia are both very large spatangoids (up to 200 mm. or more in 
length) and occur in comparatively shallow water, 1 or 2 fathoms. Metalia is much 
more flattened; the ambulacra are very slightly sunken, and the spines, especially on 
the upper side, are very coarse. Metalia is brown; Meoma varies from light- 
yellowish to deep-reddish brown. Both occur throughout the. West Indies. 
Moira atropos is easily distinguished from all the preceding by the very deeply 
sunken ambulacra, which give the test almost a deformed appearance. It reaches a 
length of 50 mm., and the color is yellowish brown. It occurs southward from 
South Carolina into the West Indies and Gulf of Mexico. 
Owing to the firm structure of the test, all echinoids (except the flexible sea- 
urchins) can stand the wearing of water for some time after the death of the animal. 
In such cases the spines drop off and the organic matter is washed out, leaving the 
tests as delicate white or (lull-colored shells, more or less granular, according to the 
size of the spines with which they were covered. These shells are sometimes called 
“ sea eggs.” Such tests are often of value to the zoologist, and should be preserved. 
Usually they are sufficient for the determination of the species to which they belonged. 
