NO. 6 NEW AMERICAN EDRIOASTEROIDEA BASSLER 1 7 



less imbricating, and the circular depressed attached theca with ambu- 

 lacra! rays i to 4 curving to the left and 5 to the right, are other 

 features of the genus. /. (Agelacrinus) cincinnatiensis (Roemer) 

 (pi. 5, fig. 11), the genotype, and one of the less rare of the edrio- 

 asteroids, was originally figured with the rays curving in the opposite 

 direction, but this was due to reversal of the image produced in draw- 

 ing with the camera lucida of that time. Wherever noted, young speci- 

 mens of Isorophus exhibit short, less curved rays and a broader oral 

 area than in the mature forms. 



ISOROPHUS TENNESSEENSIS, n. sp. 

 Plate 2, fig. I 



Theca a thin disk about 8 mm in diameter adherent to a brachiopod 

 shell {RaHnesquhia) . The species has the ambulacral and oral plate 

 arrangement of the genus, but with the oral area rather broad and 

 composed of an unusually large number of small plates and the ambu- 

 lacra shorter than usual although strongly curved. The small theca, 

 rather narrow, short, much curved ambulacra, large oral area, and 

 broad rim of marginal plates characterize this species. /. trentonensis, 

 new species, from the Trenton limestone of New York, is similar but 

 has shorter, wider little curved rays, and the oral covering plates are 

 larger. 



Occurrence. — Trenton (shaly beds in Cannon limestone), Fayette- 

 ville, Tennessee. 



Holotype.—\J.S.'^M. no. 91839. 



ISOROPHUS TRENTONENSIS, n. sp. 



Plate 5, fig. I 



As noted under /, tennesseensis, this new species differs in its short, 

 broad, almost straight, bluntly terminating arms, and in the larger 

 size of the plates forming the broad oral area. Enlarged photographs 

 bring out these differences clearly. 



Occurrence. — Trenton (upper part of Deltoidea zone), Trenton 

 Falls, New York. 



Holotype.—U.S.^.M.. no. 91843. 



ISOROPHUS (AGELACRINUS) AUSTINI (Foerste), 1914 

 Plate 2, fig. 9 ; plate 6, figs, i, 2 



This neat species is so small, (about 8 mm in diameter) that it 

 might be mistaken for the young of the larger edrioasteroids, but the 



