HEXACEINID^. 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 Bichocrinus, with 

 which, no doubt, it has some afBnities ; 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 Talarocrinus. 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. constricttis. 



PTEROTOCRINUS Lton and Cass. 



1S59. Lton and Cass.; Amev. Joiiru. Sci-, Vol. XXIX., p. 68. 



1866. Meee: and Woethen; Geol. Rep. Illinois, Vol. II., p. 288. 



1866. Shumakd ; Trans. St. Louis Acad. Sci., Vol. II., p. 394. 



1879. Wetheebt; Joum. Cincin. Soc. Nat. Hist., Vol. II. (April number). 



1879. Wetheebt; (Ak^. (October number). 



1879. Ztttel; Handb. der Palajont., Vol. I., p. 365. 



1881. W. and Sp. ; Revision Palseoor., Part II,, p. 87. 



1885. W. and Sp. ; iOid., Part III., p. 120. 



18S9. S. A. MiLLEE; N. Amer. Geology and Palaont., p. 276. 



Sjn. Jsterocrimis Lton (not Miinster 1839); Geol. Rep. Kentucky, Vol. III., p. 472. 



Calyx more or less turbinate ; the plates heavy and without ornamen- 

 tation. Dorsal cup saucer-shajDcd, 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. Eadials 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 



