HEXACRINIDiE. 755 



by an obscure groove, and similar grooves, bnt deeper, mark the interbasal 

 suture lines. Tlie processes upon the radials occupy the upper two thirds of 

 the plates, leaving their lower ends and the upper portions of the basals 

 almost free from ornamentation. The facet which supports the costals is 

 surrounded by a thickened collar, from which three — exceptionally two — 

 ridges or series of nodes pass downward ; the two outer ones in the direction 

 of the lower angles of the plates, the other following the median line. 



Basal cup large, occupying over two fifths the height of the calyx. 

 Radials considerably wider above than bolow, their length about equal to 

 their width at the upper end ; the lower faces very little convex, the upper 

 slightly excavated ; the facet directed upwards, occupying one third the 

 width of the plates ; the limbs somewhat inflected but not notched. Costals 

 two, rounded on the back, the lower very short and linear ; the second 

 a little longer and axillary, its sloping upper faces at right angles. Dis- 

 tichals three, narrower than the costals; the two lower ones combined but 

 little longer than the third, and united by sj'zygy, the second giving off a 

 strong pinnule to the outer sides of the rays; the third axillary. Arms gener- 

 ally four to the ray, occasionally five to six in one of the three anterior rays, 

 or in all of them ; they are widely divergent, comparatively' thin, rather 

 short, and composed of a single series of cuneate pieces alternately arranged. 

 Ventral disk depressed-convex, the median portions flattened and occupied 

 by five, small but well defined orals, from which five rows of comparatively 

 wide but .short covering pieces pass out to the arms. The three interbrachial 

 plates are followed by eight to ten interambulacral pieces, distributed in four 

 ranges. Anal plate a little narrower at the top than below, succeeded by 

 five small pieces transversely arranged, which in turn are followed by numer- 

 ous smaller plates forming a protuberance which contains the anal opening. 

 The anus is almost marginal and opens out laterally. Column small, round ; 

 the joints short, the nodal ones somewhat projecting. 



Horizon and Locality. — Upper Burlington limestone ; Burlington, Iowa. 



Type in the (Worthen) Illinois State collection. 



Remarks. — This species is readily distinguished from any other of this 

 genus by its peculiar style of ornamentation, in which, however, it closely re- 

 sembles Platycriniis suhsjnnulosus Hall, to which we erroneously referred it in 

 Part II. of the Revision. The type specimen, which we had examined, was im- 

 perfect, showing neither the anal plate nor the form of the calyx. Fine speci- 

 mens since obtained by us in considerable number leave no doubt that it is an 

 exceedingly well marked species, and was correctly described as a Dichocrimis. 



