NO. 6 NEW AMERICAN EDRIOASTEROIDEA BASSLER IQ 



Occurrence. — Trenton (contact between Woodburn-Greendale for- 

 mations), Lair Station, Kentucky. 

 Holotype.—U.S.^M. no. S-3967. 



ISOROPHUS SHIDELERI, n. sp. 



Plate 6, fig. 9 



This well-marked species with a theca 17 mm in diameter, equal 

 to the usual width in the genus, is readily recognized by its long, 

 much curved, extremely narrow rays made up of unusually small 

 plates and separated by many comparatively small interambulacral 

 plates. The marginal rim also, although broad, is composed of many 

 rows of small plates. Curvature of arms, structure of oral and anal 

 areas, and accessory plates on the ambulacra as in typical Isorophus. 



The specific name is in honor of Prof. W. H. Shideler, of Miami 

 University, who has collected a number of the l>est edrioasteroids 

 herein described. 



Occurrence. — Richmond (Elkhorn formation), just west of Ham- 

 burg, Indiana. 



Holotype.— U.S.N. M. no. S-3958. 



ISOROPHUS (AGELACRINUS) WARRENENSIS (James), 1883 



Plate 5, figs. 2, 3; plate 6, fig. 11 



The type of this species was poorly selected because in it the large 

 interambulacral plates are sufficiently displaced by pressure to hide 

 the ambulacra. Better specimens in the original lot, of which plate 5, 

 figure 2, represents one, show this to be a good species characterized 

 by its small diameter (13 mm) short, broad, slightly curved ambulacra, 

 large polygonal, slightly overlapping interambulacral plates, broad 

 oral area of numerous large plates, and wide marginal rim of large 

 and small plates. The dozen or more specimens in the original lot 

 maintain these characters as do specimens from other localities at the 

 same horizon. The jumbled condition that the plates may assume is 

 shown in plate 6, figure 1 1 . 



Occurrence. — Richmond, Oregonia, and near Morrow, Ohio (prob- 

 ably basal Arnheim formation) ; Clarksville, Ohio (Waynesville 

 formation). 



Holotype and plesiotype.—lJ .S.N .M. no. S-3957. 



ISOROPHUSELLA Bassler, 1935 

 The large specimen of the genotype, /. (Lebetodiscus) incondita 

 (Raymond), figured by the writer in 1935, very distinctly showed the 



