PALEONTOLOGY OF IOWA. 623 



sloping side from the adjacent radial by a small intercalated 

 plate. 



The five first radials are usually large and strong plates, 

 separated on one side by the anal plate, and broadly concave 

 on the upper side for the reception of the second radial plate. 

 Second and third radial plates smaller, the upper one a pen- 

 tagonal bifurcating plate. The arms are variously branched 

 or bifurcating. 



I have placed under this genus the following species, which appear to me to have 

 the habit and essential structure of the genus. The small intercalated plate below, 

 and to the right of the first large anal plate, is an approach to the structure of Po- 

 TERIOCRINUS as shownin the diagram given byDEKoNiNCK and LEHON. It is easy 

 to see how the small quadrangular anal plate, as shown in the figures 7 and 8 on 

 Plate xviii, in becoming enlarged, and separating the radial on that side from the 

 anal plate, may itself sustain on its upper truncated angle a second plate; thus se- 

 parating the rays by two anal plates, as in Poteriocrinus missouriensis of SHUMARD 

 ( Plate xvii, fig. 7 a, of this volume). The gradation, therefore, from CYATHOCRINUS 

 proper, as shown in C. bulletins, C. lumidus and C. proluberans ( Plate xviii ), to 

 POTERIOCRINUS, through such forms as C. spurius and C. intermedius of the same 

 plate, is very gradual, and suggests a doubt whether there may after all be reasons 

 for the generic distinction. This point, however, has been so fully discussed in the 

 memoir of DE KONINCK and LE HON, with better materials than I possess, that it 

 is quite unnecessary to introduce the question in this place. 



Cyathocrinus stellatus. 



PLATE XVI. FIG. 3 and 8. 



Cyathocrinus stellatus : TKOOST, Monogr. of Crinoideae, MS.; and Catalogue, Proceedings 

 of the American Association for the Advancement of Science, 1849, p. 61. 



BODY broad cupform, shallow, slightly contracted at the 

 upper margins. Basal plates small, acute above. Subradials 

 hexagonal ; four of them rounded on the upper oblique sides, 

 the centres produced into angular or subspiniferous nodes 

 which often project below the plane of the base, giving a 

 stellate outline as seen from below. Radial plates short, 

 tumid; upper sides straight, the articulating faces sloping 

 outwards. First anal plate quadrangular. First arm-plates 

 broad and very short. Surface finely granulose-striate. 



