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HEX ACRINIDZ. 791 
Costals very minute. Distichals 1 X 10 in the calyx; of the same proportions 
as the overlying arm plates. Arms apparently ten, their structure and that 
of the ventral disk unknown. 
Horizon and Locality. — Warsaw limestone. Found at Spergen Hill, Ind., 
Genevieve Co., Mo., and in many places in Kentucky and Tennessee. 
Remarks. — This species has been heretofore referred to Dichocrinus, with 
which, no doubt, it has some affinities; the presence, however, of a single 
very minute costal, the form and arrangement of the distichals and succeed- 
ing brachials, show distinctly its close relations with Zalarocrinus. The 
specimens vary considerably in size and somewhat in form; in most of 
them the sides of the calyx are evenly rounded, while in others they are 
contracted along the basi-radial suture. Meek and Worthen described a 
specimen of this kind as a distinct species under the name D. constrictus. 
PTEROTOCRINUS Lyon and Cass. 
1859. Lyon and Cass.; Amer. Journ. Sci., Vol. XXIX., p. 68. 
1866. Merk and Wortnen; Geol. Rep. Illinois, Vol. IL., p. 288. 
1866. Suumarp; Trans. St. Louis Acad. Sci., Vol. II., p. 394. 
1879. Werrnrrsy; Journ. Cincin. Soc. Nat. Hist., Vol. II. (April number). 
1879. WetrHurBy; did. (October number). 
1879. Zrvren; Handb. der Paleont., Vol. I., p. 365. 
1881. W. and Sp.; Revision Paleocr., Part II., p. 87. 
1885. W. and Sp.; ¢dzd., Part IIT., p. 120. 
1889. §S. A. Mituer; N. Amer. Geology and Paleont., p. 276. 
Syn. Asterocrinus Lyon (not Mimster 1839); Geol. Rep. Kentucky, Vol. III., p. 472. 
Calyx more or less turbinate; the plates heavy and without ornamen- 
tation. Dorsal cup saucer-shaped, wider than high; the ventral disk py- 
ramidal, higher than the cup. The disk has five very large conspicuous 
plates or processes disposed radially, which in the form of wings or horns 
pass out from between the arms. 
Basals two, both pentagonal; the suture passing from the posterior to 
the anterior side of the calyx. Basal cup shallow, and upon the posterior 
and anterior sides angularly excavated for the reception of the anal plate 
and the anterior radial. Radials wider than long, rapidly increasing in 
width upwards; subquadrangular in outline, except the anterior one, which 
is angular below, while the others are truncate; the superior faces slightly 
undulated. Costals but one to the ray, which is often hidden from view, and 
is always minute and triangular. It supports two distichals, both axillary, 
which meet over the apex of the costal, their lateral faces resting upon the 
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