30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



This species was found at stations 17, 17a, 18, 19, 20, 21, 22, 23, 30, 

 36, 37, 39, 43, 44 (dead), 49, 53, 57, 58, and 61. 



Behavior. — Clypeaster subdepressus burrows through grassless 

 sand with its dorsal surface buried as deeply as 1 inch below the 

 surface, or it moves along the top of the sand in areas where various 

 algae tend to bind the sand, or where much of the sand is composed of 

 coarse shell fragments. When it remains unburied, moving upon the 

 surface of the sand, it covers itself with a layer of sand, shell frag- 

 ments and other debris which it carries along as it moves (pi. 6, fig. 8) . 

 Normally shell fragments, leaves, or other coarse material are carried 

 over the apical area, and finer sand over the remainder of the test. 



When excavated from the sand, this species can re-bury or re-cover 

 itself in about 6 to 12 minutes. The speed of burial, and of righting 

 when overturned, seems to be related to size, with the smaller speci- 

 mens accomplishing these activities somewhat faster than the larger 

 ones. The manner of re-burial is illustrated on plate 5, figures 1-6, 8. 

 The animal begins to move forward slowly, at the same time bringing 

 sand up over the anterior and anterolateral parts of the test by means 

 of the numerous locomotor spines that are abundant around the pe- 

 riphery, and the podia that are concentrated in the ambulacral areas of 

 the dorsal surface, distal to the tips of the petals. The major portion 

 of the sand on the test is brought up along these anterior areas, but at 

 the same time the podia in the areas behind the two posterior petals 

 also bring up sand grains in thin layers. The main two sheets of 

 sand move back, coalescing with one another along the midline of the 

 test, while two smaller, thinner sheets of sand move anteriorly from 

 the posterolateral corners. Thus the test is effectively buried when all 

 the sand sheets meet, which is accomplished before the animal has 

 moved forward its own length. 



This species can right itself after being overturned, although it does 

 this in a different direction and at a slower rate than either Leodia 

 sexiesperforata or Europe michelini. Small specimens manage to 

 right themselves significantly faster than large ones. In one experi- 

 ment where three specimens were placed near one another on their 

 dorsal surfaces, a small one turned itself over and was buried before 

 two larger ones raised themselves to 45 degrees (pi. 6, figs. 1-6). 

 Sand is brought up onto the oral surface of an overturned specimen 

 by the locomotor spines at the periphery, and the podia in the ambu- 

 lacral areas. The sand comes up along one side, or one anterolateral 

 area, thus this side is dug down into the sand. As it digs, increasing 

 numbers of locomotor spines and podia on the oral surface are 



