l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



photographic illustrations show it to have characteristics of typical 

 mature Isorophus, differing from other species in the delicacy of its 

 parts and its short, narrow recurved rays. One of the original types 

 and a specimen more robust than usual, as well as an example show- 

 ing the under side of the theca, are here illustrated. 



Occurrence. — Richmond (Whitewater formation), Dutch Creek, 

 4^ miles northwest Wilmington, Ohio, Fallen Timbers Creek, Ver- 

 sailles, Indiana, and Dodge's Creek, Oxford, Ohio. 



Cotypes and plesioty pes. ~IJ .S.N M'. nos. 70162, S-3961, S-3963. 



ISOROPHUS (AGELACRINUS) HOLBROOKI (James), 1878 

 Plate 5, figs. 8, 9 



This, the most striking species of the genus, is characterized by its 

 large size (diameter, 30-40 mm), semiglobose to hemispherical shape, 

 numerous rows of little imbricating interambulacral plates, and the 

 long, comparatively narrow, ambulacra recurving strongly along the 

 edge of the theca. 



Occurrence. — Richmond (Arnheim formation). Morrow, Ohio. 



Plesiotype. — U.S.N.M. no. 40744. 



ISOROPHUS GERMANUS, n. sp. 



Plate 6, figs. 3, 4 



Closely related to /. holbrooki and probably a derivative of it, agree- 

 ing in its semiglobose theca (20 mm wide) and other characters, but 

 differing in the fewer number of plates in all the interambulacral 

 areas and in the less definite arrangement of the anal plates. 



Occurrence.— Kichmond (Waynesville-Clarksville division). Mor- 

 row and Oxford, Ohio. 



Cotypes. — U.S.N.M. nos. S-3959, S-3960. 



ISOROPHUS ICENTUCKYENSIS, n. sp. 

 Plate 6, fig. 10 



Theca a subhemispherical disk 25 mm in diameter, with the general 

 characters of Isorophus and related to /. holbrooki but differing in 

 that the arms are shorter, less recurved, and the interambulacral plates 

 are smaller, less regular, and more imbricating. 



Although undoubtedly a new species, the type specimen is crushed 

 and not well enough preserved to show the fine details of the surface. 



