ECHINODERMATA OF THE BRASSFIELD FORMATION 
25 
of inframarginals which is exposed immediately adjacent in case 
of any of the rays. In ray II, the inframarginals are in contact 
with supramarginals as near as the sixth supramarginal, not 
counting the basal plate of this series. In ray I, they are in con- 
tact as near as the fifth supramarginal. On the sinistral side 
of ray V, the nearest inframarginal alternates with the sides of 
the fourth and fifth supramarginal. This suggests that if any 
ambitals exist the latter must be restricted to more proximal 
parts than any here exposed and that their number must be small. 
The actinal side of the rays is exposed by the tip of ray V (see 
figure VB on plate IV) for a length of 15 mm. The inframarginal 
plates form the sides of the rays and the adambulacral plates 
form two additional rows, one on each side of the ambulacral 
groove. In number, the adambulacrals appear to equal the 
inframarginals, and to be directly opposite the latter, but they 
are of less width. The plates seen at the bottom of the ambu- 
lacral groove are interpreted as ambulacral plates, but they are 
not exposed well enough to permit of accurate description. 
The surface of the plates, where unweathered, is minutely 
granular, about four granules occurring in a distance of half a 
millimeter. 
Locality and formation. Five and a half miles west of Hills- 
boro, Ohio, at a quarry reached by going from Fairview cross- 
roads half a mile east and then three-quarters of a mile south- 
ward, to the southern side of the head-waters of a small stream. 
Here, the specimen described, a holotype, was found in the thin- 
ner-bedded layers at the top of the quarry, associated with 
Brockocystis nodosarius, Hallopora magnopora, Orthis flahellites, 
Strophonella daytonensis, and Plectambonites transver satis. These 
thin-bedded hmestone layers occur II J feet above the base of 
the quarry. The base is formed by the more massive cherty 
layers which occur a short distance above the base of the Brass- 
field formation. Named in honor of Prof. Charles Schuchert, 
in recognition of his many services to American Paleontology. 
Remarks. The most striking feature of Mesopalaeaster s chuck- 
erti consists in the radial plates forming a distinctly recogniz- 
able series only along the more distal parts of the rays, and in 
