ECHINODERMA TA—ECHINOIDEA . 591 



XVIIL Periarchus Conrad. 

 Scutelloid, with central apex more or less abruptly elevated, 

 short ambulacra open at the ends, and extending only half way to 

 the margin; periproct on under side nearer the mouth than the 

 margin. Eocenic-Oligocenic. 



2y. P. lyelli (Conrad). Eocenic-Oligocenic. 



Margin thin, gently concave for less than one fourth the diam- 

 eter, rising abruptly in center to apical system ; ambulacra uniform ; 

 length a little more than one fourth the diameter of test, actinal 

 surface flat; grooves bifurcating; diameter 80 mm. 



Claibornian of Alabama; Vicksburgian of Georgia. 



XIX. ScuTELLA Lamarck. 

 Test very flat, subcircular in outline, sometimes undulating or 

 notched, broadest behind. Ambulacral furrows branching ; petaloid 

 part of ambulacra unequal, well-developed, nearly closed; peri- 



/■ 



Fig, 1923. Scutella albei'ti^ upper, lateral and lower view, X Yi- (Md. Survey.) 



stome small, central, subcircular; periproct very small, mostly 

 inframarginal ; apical system central, more or less pentagonal. 



Tertiary. 



28. S. alberti Conrad. (Fig. 1923.) Miocenic. 

 Discoidal, orbicular, very much depressed, but swelling towards 



the middle, and depressed at apex; diameter 160 mm. X 150mm. 

 Chesapeakean (Choptank) of Maryland. (Abundant.) 



29. S. fairbanksi Merriam. Miocenic. 

 Smaller than preceding (maximum diameter 36 mm.), broadest 



posteriorly; margin scarcely notched. 



Lower Miocenic (Vaqueros formation) of California. 



