no. 5 



TERTIARY ECHINOIDS FROM FLORIDA — KIER 



31 



Table 1. — Dimensions of 6 specimens of Clypeaster crassus Kiev, new species 



Florida 



South Carolina 



Length 

 91 

 121 

 141 

 101 

 110 

 126 



Width 

 85 

 108 

 121 

 89 

 101 

 115 



Height 

 15 

 20 



18 



21 

 27 



Thickness 



of margin 



8.3 



9.8 



12.0 



8.2 



10.1 



11.5 



Number of 



pore-pairs 



Petal 



III II I 



60 58 55 



71 

 67 

 67 

 64 



64 

 63 

 57 

 61 



69 

 62 

 60 

 65 



III 



26.3 

 38.5 

 45.0 

 32.5 

 34.5 

 41.0 



Length of 

 petal 

 II 

 24.9 

 32.5 

 35.7 

 29.0 

 29.6 

 37.7 



I 



24.8 

 33.3 

 38.5 

 29.0 

 30.3 

 39.0 



Peristome. — Central to slightly posterior, pentagonal, pointed an- 

 teriorly, truncated posteriorly. 



Adoral plate arrangement. — Plate sutures of basicoronal plates not 

 visible on all plates ; basicoronal interambulacral plates separated 

 from postbasicoronal plates by two pairs of ambulacral plates (text 

 fig. 24) ; 7 to 8 ambulacral, 3 to 5 interambulacral postbasicoronal 

 plates in each series on adoral surface. 



Comparison with other species. — C. crassus is very similar to the 

 living species Clypeaster prostratus and is probably an ancestor of it. 

 It is similar in shape, size, petal arrangement, plate arrangement, and 

 position of apical system, periproct, and peristome. It differs mainly 

 in having a thicker margin. In C. crassus the margin is 10 percent 

 of the length, whereas in the average specimen of C. prostratus it 

 is 7.2 percent of the length. In C. crassus the interambulacra are 

 much more strongly indented at the margin in areas 4, 5, 1, and the 

 poriferous zones are slightly wider. 



Fig. 24. — Clypeaster crassus Kier, new species : Adapical and adoral views of 

 U.S.N.M. 648176, from Intracoastal Waterway Canal about 5 miles southwest 

 of Little River, Horry County, S. C, X i- Basicoronal plate sutures not visible. 



