BATOCRINID^. 539 



wliicli decrease in size ujDwards. Interdistichals one or two, placed longitudi- 

 nally. Ventral disk hemispherical ; the plates nearly flat and of irregular 

 arrangement ; orals and radial dome plates a little larger and convex. 

 Anus siibcentral. Column strong, the axial canal large and obtusely pen- 

 tangular. 



Horison and Locality. — Hamilton group, New Buffalo, Iowa. 



Megistocrinus Parnsworthi (White). 

 Plcde XL VIII. Fiffs. 4:a, h. 



1876. White ; Proceed. Acad. Nat. Soi. Phila., p. 29. 

 1881. W. and Sp. ; Eevisioa Pateocr., Part II., p. 138. 



Of moderate size. Calyx subglobose, nearly as high as wide; the lower 

 portions of the dorsal cup to the middle of the first costals truncated, the 

 sides almost at right angles with the base, very slightly expanding to the 

 arm bases, the latter somewhat projecting; the plates convex and without 

 ornamentation. 



Basal disk proportionally large, slightly projecting; the central part 

 a little excavated for the reception of the column ; axial canal rather large 

 and obtusely pentangular. Radials horizontal, smaller than the costals. 

 First costals abruptly curved ; the lower end of the plates on a level with the 

 radials, the upper ends vertical. Distichals three in the two antero-lateral 

 rays ; in the three other rays but one, which being axillary is succeeded by 

 2X4 palmars. Arms sixteen, arranged in groups of two and four; the arm 

 bases a little projecting. Interbrachials : 1, 2, 2, 3, followed by several 

 smaller pieces between the arm bases. The first anal plate, which is a little 

 narrower than the radials, succeeded by rows of three, four, and six pieces, 

 with numerous irregularly arranged plates above. Interdistichals two to four, 

 the lower one sometimes touching the costal axillary. Yentral disk high, 

 slightly conical ; composed of rather large pieces. Orals completely isolated 

 by supplementary pieces ; they are larger than the surrounding plates, but 

 not more prominent. Anus subcentral. 



Horizon and Loccdii//. — Hamilton group ; Solon, Iowa. 



Ti/2}e-s in the Museum of the State University at Iowa City. 



