28 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I45 



Apical system. — Central, monobasal, madreporite pentagonal, geni- 

 tal pores small, five, varying in position from adjacent to madre- 

 porite, or far distant, occurring in interambulacra. 



Ambulacra. — Petals all similar, broad, closed, long petals II, III, 

 IV extending almost to margin, petals V, I over two-thirds distance 

 to margin; number of pore-pairs in each poriferous zone variable; 

 pore-pairs near apical system extremely small, difficult to see ; porifer- 

 ous zones only slightly depressed relative to interambulacra. 



21 



2Z 



20 



Figs. 20-22. — Clypeaster rosaceus dalli (Twitchell) : 20, Adoral view of 

 U.S.N.M. 648164; 21, right side of U.S.N.M. 648165; 22, right side of U.S.N.M. 

 648166. All from the Caloosahatchee formation, loc. 6. All X i- 



Periproct. — Small, inframarginal, situated within 1 or 2 mm of 

 posterior margin, at junction between fourth and fifth postbasicoronal 

 interambulacral plates. 



Adoral interambulacra. — Primiordinal interambulacral plates much 

 smaller than ambulacral plates (text fig. 20), separated from post- 

 basicoronal plates by two pairs of ambulacral plates; 9 or 10 post- 

 basicornal plates in each interambulacrum adorally; 16-20 plates in 

 each ambulacrum. 



Peristome. — Central to slightly posterior, deeply depressed, circu- 

 lar to slightly pentagonal, opening 10 mm wide on specimen 100 mm 

 long. 



