ACTINOCRmiD^. 557 



Actinocrinus lobatus Hall (not Woethex). 

 Plate LII. Figs, la, l, and Plate LIV. Fig. 3, ami Piute LV. Figs, la, h. 



I860. HiLL; Siippl. GeoL Rep. Iowa, p- 51. 



1881. W. and Sp. ; Revision Palseocr., I'ait II., p. 144. 



(V) Syn. Actinocrinus unicarinatus — Hall; Suppl. Geol. Rep. Iowa, 1800, p. 48. 



Larger than the preceding species ; the lobes of the calyx more promi- 

 nent ; the interradial spaces deeper, and formed into pitlike depressions, 

 which extend from the upper part Cif the first interbrachial to near the orals, 

 reducing the width of the teguien, with the brachial lobes removed, to the 

 diameter of the dorsal cup at the radials. The dorsal cup rises moderately 

 to the top of the first costals, above which the brachials take an almost hori- 

 zontal position to the bases of the free arms. The lobes are narrower at the 

 proximal than at the distal end, and at the back of the costals distinctly 

 angular, their sides bending abruptly upwai'd to meet the small interbrachial 

 pieces interposed between them. In the lower part of the calj'x, below the 

 lobes, the plates are slightly tumid, having small central nodes, of which 

 those upon the ra,dials and costals are most prominent and transversely 

 arranged. From the nodes, sets of parallel ridges proceed to the outer 

 margins; but these, although quite distinct between basals and radials, are 

 more or less obscure between the other plates. 



Basals proportionally large, forming a broad cup, twice as wide as high, 

 notched at the sutures, and thickened around the lower margins. Radials 

 very large, longer than wide, the upper fiice narrower than any of the 

 others. Costals small, the two together less than one half the size of the 

 radials ; the first as wide as long ; the second as wide as the first, but 

 shorter. Distichals nearly one third smaller than the upper costals, all 

 axillary. They support at the outer side an arm, which is free from the 

 second plate ; at the inner side three palmars, which give off an arm to the 

 inner side of the ray, and to the outer two post-palmars with two free arms 

 from the axillary. Arms forty (not twenty-five as described by Hall), moder- 

 ately heavy, and branching in their free state. Interbrachials numerous ; 

 the first as lai^ge as, or larger than, the first costals ; the two of the second 

 row one half smaller; there are other irregular plates overlying them, which 

 meet the orals, and are in part interambulacral. Anal interradius the widest, 

 and the plates still more numerous. The central part of the tegmen is almost 

 flat, and raised but little above the top of the lateral extensions; its plates 



