38 LARVIFORM CRINOIDS 



an anomalous appearance as though the lower part of the calyx had been 

 twisted. 



The large anal opening is situated in a deep scallop in the upper right- 

 hand corner of the posterior basal. It lies largely within this plate but is 

 also bordered by the right posterior basal, and the posterior and right posterior 

 orals. 



The oral dome covers the entire ventral surface of the calyx and con- 

 stitutes about one-fourth its height. The oral plates are triangular above 

 except for the posterior one whose upper angle is notched to receive the ends 

 of the anterior orals. The upper surfaces are flat but the edges are rather 

 sharply upraised and the orals meet along five radiating ridges. At the edge 

 of the ventral surface the oral plates bend sharply downward to meet the 

 basals below. 



The entire surface of the holotype is covered with comparatively large 

 but unequally sized and irregularly arranged pits. They are largest and 

 most conspicuous on the oral plates and decrease notably in size or are absent 

 near the sutures which in this way only are distinguishable. 



Remarks. — I have included in a single series a considerable number of 

 specimens ranging in size from about .5 mm. to the holotype which is the 

 largest, considering the smaller ones to be immature examples. The second 

 specimen figured on Plate II (9d) is the second largest. This and the 

 holotype alone show the lateral anal opening, and were there not two speci- 

 mens this opening would have been considered an accidental break, so pecu- 

 liar is its situation. The smaller specimens also differ from the larger in 

 not being so conspicuously pitted, nor is the twisting of the calyx apparent 

 in them. This series seems to show that the displacement of the orals and 

 the appearance and displacement of the anal opening are features which were 

 progressively developed during the growth of this crinoid, substantiating a 

 similar opinion formed by Jakovlev [6] from a study of a large number of 

 specimens of Hemistreptacon. 



Occurrence. — These silicified specimens were obtained from a limestone 

 near the base of the Pennsylvanian section in the center of the N. */> sec. 35, 

 T. 21 N., R. 9 W., Warren County, Indiana. 



