HEXACRINID^. 757 



the summit somewhat flattened and covered by large orals, from which two 

 rows of tuberculous covering pieces pass out to the arms. Interradial spaces 

 slightly depressed and paved by numerous rather large plates, all having 

 a small tubercle in the centre ; the anal interradius has five plates in the 

 first row as against -three at the otlier sides, and is very wide and bulging, 

 the plates throughout being large, except those immediately surrounding the 

 anus. The anal opening is placed near the summit in close proximity to the 

 posterior oral. Column round, of moderate size, slightly tapering downward, 

 the nodal joints but little wider than the internodals. 



Horizon and Locality. — Keokuk limestone ; Crawfordsville, Ind. 



Types in the collection of the late Major Sidney S. Lyon, Jefferson- 

 ville, Ind. 



Remarks. — Dicliocrinus expansus Meek and Worthen is undoubtedly iden- 

 tical with this species, although the sj)ecimen figured has only six arms to 

 the ray. Moreover, that name was pre-oecupied hy De Koninck and Le 

 Hon in 1853. 



Dichocrinus striatus 0. and Shum. 



Plate LXXVn. Figs. Ua, h. 



1S53. Owen and Shtjitaed ; U. S. Geol. Eep. Wise, Iowa, and Minn., p. 590, Plate 5A, Tigs. 10«, b. 

 1S81. W. and Sp. ; Revision Palseocr., Part II., p. 85. 



Calyx subglobose, widest at the basi-radial suture ; composed of thin 

 plates, which are thickly covered with conspicuous, abruptly elevated, longi- 

 tudinal ridges. These ridges form around the calyx six well defined rhombs, 

 which meet interradially at the basi-radial suture, the acute upper angles of 

 five of them reaching to the radial facets, that of the sixth to the upper part 

 of the anal plate, and their lower angles to the lower ends of the basals. 

 The rhombs are subdivided into two triangles by the basi-radial suture, and 

 the included spaces are occupied by three or four vertical ridges, often with 

 smaller ones between, which all cross the suture line unbroken. Other 

 ridges, but less distinct and easily overlooked, fill the triangles formed 

 between the upper sides of adjoining rhombs,, and these as well as those 

 within the rhombs, when examined under a lens, have an imdulated outline. 



Basal cup hemispherical, slightly truncated at the lower end ; column 

 facet well defined and bordered by the lower ends of the ridges; height equal 

 to that of the radials; superior margin distinctly hexangular. Eadials quadri- 

 lateral, narrower at the top than at the bottom; the width at the lower faces 



