8 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 121 



Clypeaster rosaceus (Linnaeus) 



Three dead tests were found at a depth of 25 feet in one of the sandy 

 patches in the rocky-coral areas in association with Clypeaster sub- 

 depressus and Meoma ventricosa (Lamarck). 



Leodia sexiesperforata (Leske) 



This species was found hving on the sandy areas in the bays in 

 depths from 5 to 20 feet. The animal lives completely buried under 

 2 to 4 inches of silty sand. The echinoid makes no track in the sand 

 visible on the upper surface of the sea bottom. In most cases the 

 ripple marks on the bottom continue uninterrupted directly over 

 the spot where the echinoid is buried. The only clue to the presence 

 of living specimens is the occurrence of dead tests at the surface. 

 In most places it occurs with no vegetation although in some areas 

 a small amount of eelgrass is present. 



Meoma ventricosa (Lamarck) 



Plate 2 (figs. 1-3) 



Although not abundant, this species was found in sandy patches 

 in every coral-rock environment from depths of 15 to 85 feet. Pre- 

 sumably it occurs at greater depth off Dominica but no dives were 

 made below 85 feet. In other areas in the West Indies it has been 

 dredged from depths down to 600 feet. It is not conspicuous on the 

 bottom because it covers itself with sand and fragments of coral or 

 weed. It would not be correct to say that it buries itself in the 

 sediment, for only approximately one-fifth of its test is below the 

 general level of the surrounding substratum. Rather than pushing 

 itself under the sediment, the animal pulls the sediment over itself 

 with its spines and tubefeet. Generally, larger fragments of coral 

 are concentrated around the apical system (pi. 2 : fig. 1) . Presumably, 

 the echinoid avoids placing small objects in the area of his madreporite. 

 Although usually covered with sediment, the echinoid can be found 

 because of the sorting of this sediment over the test, the large mound 

 it makes on the bottom, and the lighter color of the sediment on the 

 test. Furthermore, the echinoids leave a conspicuous track (pi. 2: 

 fig. 3), usually two to three feet long, consisting of a furrow with a 

 smaU ridge of sand on each side. 



The echinoids do not occur in great density. On the average, 

 four to six specimens occur in an area of 100 square ft. These sandy 

 patches are usually 1-300 square feet in area and occur quite com- 

 monly in the coral-rock areas. Although similar sediment occurs 

 in the noncoral tracts, this echinoid was never found there. At 

 every station except one no weed or large algae was hving in the sandy 

 patches with the echinoids. The one exception occurred at a locahty 



