28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 149 



of echinoids, are necessary before it can be concluded that the habit 

 of covering is for one purpose only, or that it is for the same purpose 

 in all species. The cover of debris employed by C. rosaceus is 

 elaborate compared to that of L. variegatus (pi. 3, fig. 1 ), and no mat- 

 ter what the triggering mechanism may be (e.g. sunlight) the debris 

 serves as a remarkably effective camouflage, at least to the human eye. 

 Species in which the covering habit has been studied drop the shells 

 and grass each night, and pick up a new supply each day shortly after 

 sunrise (summary in Nichols, 1964, p. 406). If C. rosaceus also does 

 this, it would greatly enhance the effectiveness as camouflage, as local 

 objects would be picked up each day. As mentioned above, individuals 

 observed in grass used grass for cover, those on shelly sand used 

 shells ; all seemed to employ sand grains to a minor extent. 



CLYPEASTER SUBDEPRESSUS (Gray) 



Plate 5, figures 1-6, 8; plate 6, figures 1-10; plate IS, figure 8; text figure 6 



This echinoid has a large, low test with only slightly inflated petals, 

 a flat lower surface, and is yellow brown to tan in color when alive. It 

 has no perforations (lunules) or indentations at its margin, which im- 

 mediately distinguishes it from the sand dollars with which it is often 

 associated. It differs from Clypeaster rosaceus of this genus which is 

 often found nearby, in its flattened test with less inflated petals, flat 

 lower surface, and lighter color. 



Occurrence. — Clypeaster subdepressus was found in sandy areas 

 with little or no grass or filamentous algae, normally where the sand 

 was deep. Isolated specimens were encountered in small sandy basins 

 within reefy areas where only 6 to 8 inches of sand overlay hard sub- 

 strate. Apparently it prefers depths somewhat greater that those nor- 

 mally inhabited by the sand dollars, Leodia sexiesperforata and En- 

 cope michclini, because it is not consistently present on the broad 

 sandy expanses in shallow water on the White Bank. Instead it is most 

 frequent in the large sandy areas of the "interreef deep channel" in 

 depths between 15 and 35 feet (fig. 6). Relatively small dead tests 

 were abundant around the nests of burrowing fish, offshore from the 

 reef at depths as great as 85 feet; living specimens were rare and 

 small at that depth. The limits of depths at which live or dead speci- 

 mens of this species were encountered are 12 and 85 feet, although the 

 greatest abundance of living specimens occurred between 15 and 

 35 feet. 



