66 The Ohio Journal of Science [Vol. XXI, No. 2, 



median part of each radial curves conspicuous outward for a distance of 

 about one millimeter. Near mid-height of the radials the cross-section 

 of the theca is pentagonal but along the basals this cross-section changes 

 to triangular, as in other species of Troostocriniis. 



In the type (Plate III, Fig. 3A), the distance between the base of 

 the radials and the lower end of the ambulacra is 17 mm., and from the 

 latter to the acute tip of the areas between the sinuses the distance is 

 about 11 mm. The lateral diameter of the theca just beneath the 

 projecting lower ends of the sinuses is 15 mm. The basals diverge rather 

 strongly, as in figure 3B on Plate III. The divergence of the lower part 

 of the radials is much less, giving rise to the specific name subcylindrica. 

 In another specimen (Plate III, Fig. 3C), recently found at Cedarville, 

 Ohio, the theca is much more elongate. 



Locality and Horizon. — From the Cedarville dolomite. 

 The type, numbered 3306, accompanied by the basal part of 

 another specimen, is in the Museum of Ohio State University; 

 both specimens were obtained at Yellow Springs, Ohio. A third 

 specimen, here figured, was obtained in the quarry at 

 Cedarville, Ohio. 



Remarks. — Troostocriniis suhcylindricus is characterized by 

 the strong outward curvature of the median part of the radials 

 immediately beneath the lower end of the radial sinuses. This is 

 shown conspicuously on lateral view. 



In Troostocriniis reinwardti, from the Brownsport formation 

 of Western Tennessee, there is no corresponding outward cur- 

 vature of the median part of the radials. On the contrary, on 

 lateral view the median parts of the radials curve slightly 

 inward rather than conspicuously outward just before reaching 

 the lower end of the radial sinuses. The length of this convex 

 curvature is only about one millimeter. Moreover, the lower 

 third of the theca usually is much more slender, the lower half 

 of the radials diverging more strongly. In the Brownsport 

 species, the side-plates number about 16 in a length of 5 mm. 

 The surface of the ambulacra, compared with that of other 

 species, is distinctly flattened, the groove between the series of 

 side-plates being not consicuous, nor straight, but zigzaging 

 rather strongly between the alternating side-plates. 



IS. Troostocrinus sp. 



(Plate I, Fig. 15.) 



Only a single specimen of Troostocriniis is known from the Chicago 

 area. This specimen is numbered 221)07 in Walker Museum at Chicago 

 University, and is from Bridegport, Illinois. It evidently is from the 



