48 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



This species was found at stations 17, 17b, 19, 20, 21, 22, 23, 24 

 (dead), 27, 29, 30, 36 (dead), 37, 39, 44, 45, 49, 51, 52, and 53. 



Behavior. — Meoma ventricosa burrows through the sand with the 

 dorsal surface of the test covered to a depth of as much as 1.5 inches. 

 Most dig less deeply than that, and many keep the uppermost part of 

 dorsal surface nearly at the surface of the sand. These sort the sand 

 slightly, to keep relatively coarse grains and shell fragments over the 

 petal areas, and are visible from above (pi. 11, fig. 6). Some speci- 

 mens seemed to burrow steadily through the sand, leaving even trails, 

 each with a narrow row of coarse sand in the middle. Others appar- 

 ently moved more sporadically, leaving trails that consisted of con- 

 nected series of low mounds marking where individuals repeatedly 

 stopped and again moved forward. 



Some specimens were found in areas of dense turtle grass (pi 3, 

 fig. 4), where the tangled root systems made burrowing impossible. 

 These were smaller than the average adult living in clean sand, and 

 they lived above the surface of the sand covered with shell fragments, 

 sand grains, and a few blades of grass, much in the manner of Cly- 

 peaster rosacens, and associated with that species. Blades of turtle 

 grass were preferred for cover by C. rosaceits in grassy areas, but in 

 the same areas M. ventricosa used mostly sand and coarse sand size 

 shell fragments, and only a few blades of grass (pi. 3, figs. 4, 5). 



When excavated and placed on the surface of the sand, M. ventri- 

 cosa buries itself without moving forward. It brings sand laterally 

 away from the ventral surface (pi. 11, figs. 4, 5), and up along the 

 sides, thus displacing the sand and moving the test directly downward 

 into the sand. The displaced sand forms two low, crescent-shaped 

 mounds, one on each side, and these ultimately coalesce over the dorsal 

 surface of the test. However, before they meet, the test is already 

 effectively covered by a thin layer of sand that has been brought up 

 onto the petal area (pi. 11, fig. 5). The process of burial is lengthy, 

 and gradually slowing. The excavated animal is reburied to about 

 half its height in about 7 to 9 minutes, but only about 75 percent cov- 

 ered after 20 minutes. From then the process slows even further, al- 

 though the test may be effectively covered by the thin layer over the 

 petals after about 30 minutes. The individual is buried to "burrow- 

 ing depth" after 40 to 50 minutes, and then may begin to move for- 

 ward. This process is much slower than the reburial of the thin sand 

 dollars Encope michelini and Leodia sexiesperforata, and also some- 

 what slower than that of the thicker form, Clypeaster subdepressus. 

 It is also much slower than the burial process of the similarly large 



