PLATE 21. 



Lepidocentrus drydenensis (Vanuxem). Page 288. 



Fig. 1. Same specimen as photograph, Plate 16, fig. 5. Holotype. X 0.9. Internal mold with the superposed combina- 

 tion of some external characters. Ventral view, ambulacra are narrow, plates low. Interambulacral areas with 

 apparently nine columns of plates which are ill denned as indicated by dotted lines, for the impression is weak. 

 Acicular spines in place and also in the adjacent matrix, peristomal area small. 



Fig. 2. Same specimen. X 3.6 Ambulacral plates with pores, from area D of fig. 1. 



Fig. 3. Same specimen. X 3.6. Ambulacral plates from area B, showing the number apposed to an adradial plate. An 

 X in figs. 1, 2, 3 indicates the location of the enlarged figures. 



Lepidocentrus whitfieldi sp. nov. Page 290. 



Fig. 4. Same specimen as photographs, Plate 19, figs. 6, 7. Holotype. X 1.8. Ventral view, internal mold. Ambulacra 



narrow, plates low. Eleven columns of interambulacral plates in an area. A primordial interambulacral plate is 



in place in the basicoronal row. 

 Fig. 5. Same specimen. X 1.8. Dorsal view, genital plates have numerous pores, ocular plates restored as indicated 



by dotted lines. The apical disc though incomplete is evidently small proportionately to the diameter of the test. 



This is the only specimen known in the genus Lepidocentrus which shows the plates of the apical disc (p. 287). 



Hyattechinus rarispinus (Hall). Page 292. 



Fig. 6. Waverly Group, Lower Carboniferous, Meadville, Pennsylvania. Amer. Mus. Nat. Hist. Coll., 6,392. Holotype. 

 X 1.8. External sandstone mold of the dorsal side, so that the lettering is reversed. Ambulacra are narrow, plates 

 low, eleven columns of interambulacral plates in each area, the eleventh introduced above the ambitus, columns 1 and 

 2 drop out dorsally. Same specimen as photograph, Plate 22, fig. 7. (See pp. 294, 395.) 



