NO. 6 ECHINOID DISTRIBUTION AND HABITS — KIER, GRANT 3 1 



brought into contact with the sand, and as that side digs in, the other 

 is raised. It takes 45 minutes to an hour to achieve a vertical position, 

 but once that is achieved, the remainder of the turnover, and complete 

 burial are accomplished in an additional 5 to 15 minutes. 



This sidewise method of overturning contrasts to that of Leodia 

 sexiesperforata and Encope michelini which right themselves by turn- 

 ing on their anterior edges. Reasons for the differences probably are 

 in the shapes of the tests, and the patterns of concentrations of spines. 

 L. sexiesperforata and E. michelini are essentially circular, or at least 

 their anterior portions are evenly arcuate. C. subdepressus is elongate, 

 narrowest at the anterior, and has long, relatively straight sides with 

 numerous locomotor spines along the edges, and in two interambu- 

 lacral concentrations that radiate to the sides. The petal area of 

 C. subdepressus projects high above the major portion of the test, 

 and an overturned specimen that rests on this high convex hump tends 

 to lean to one side. If all spines move, those in contact with the sand 

 will begin to dig in, and they are the spines along the down side of the 

 tilted test. 



Family MELLITIDAE Stefanini 



Genus LEODIA Gray 

 LEODIA SEXIESPERFORATA (Leske) 



Plate 7, figures 6-8 ; text figure 7 



This sand dollar is characterized by its very low test with thin 

 margins, six slotlike lunules, and short petals of equal length. An 

 adult is approximately 80 mm. in horizontal diameter and is yellow to 

 light brown when alive, white when dead and denuded of spines. It 

 differs from the other sand dollar associated with it, Encope michelini, 

 in having a smaller thinner test, lighter color, shorter petals, and six 

 perforations, rather than the five indentations and one perforation of 

 E. michelini. 



Occurrence. — Leodia sexiesperforata was found in areas of open 

 sand where grass and filamentous algae were scarce or absent. The 

 sand normally was rather deep (at least 1 foot) and at most localities 

 its surface was strongly rippled, although on calm days the ripples 

 were rapidly destroyed by burrowing of this and other species of 

 echinoids. The species was most abundant on the broad calcareous 

 sand expanses of the White Bank, nowhere as abundant as the other 

 discoid species, Encope michelini and Clypeaster subdepressus 



