688 GEOLOGICAL SURVEY OF IOWA. 



protuberances which are gradually narrowed towards the 

 summit of the plate. First radial plates pentagonal ( except 

 one on the anal side which is quadrangular), protuberant in 

 the centre. Second radial plates small (imperfect in the 

 specimen described). Anal plates two; the one truncating 

 the subradial plate, small, a large unequally pentagonal plate 

 lying obliquely between the truncated subradial plate and 

 the adjacent radial, and reaching as high as the top of the 

 latter, its lower shorter side resting against the adjacent 

 subradial on the right. 



This species is remarkable for the broadly rounded basal depression and the pro- 

 minent angular extension of the subradial plates, giving to this part a stellate or five- 

 lobed form; while the first radials alternate in five more rounded protuberances, 

 lying above, and in a line with the depressions between those below. 

 Fig. 5 a. Basal view of the specimen. 



Fig. 5 b. View of the anal side of the same, showing the protuberant form of the plates. 

 FIG. 116. 



The accompanying diagram illustrates the form 

 and proportions of the plates of this species as 

 far as the first radial plates. Most of the impres- 

 sions of the engraved plates erroneously represent 

 the subradial plates as extending to the centre : 

 this error is corrected in the diagram. 



P 



Geological position and locality. In the Kaskaskia limestone : Pope 

 county, Illinois. 



The body of this species is very similar to that described by Mr. S. S. LTON, in 

 the Geological Report of Kentucky, as Graphiocrinus 14-brachialis (the anterior ray 

 having two arms and the others each three) ; and I observe now for the first time 

 that he expresses a doubt whether the basal pieces, of the formula of DE KONINCK 

 and LE HON, are the true basal pieces. The specimen under consideration has cer- 

 tainly five plates within the larger protuberant ones, and the form of the anal plates 

 has induced me to refer the species to the Genus CTATHOCBINUS. It differs from C. 

 stellatus of TROOST in the deeper basal depression and the more obtusely protuberant 

 subradial plates, and it may prove more nearly allied to Zeacrinus than to Cya- 

 thocrinus. It is possible that the present species will prove identical with the one 

 described by Mr. LTON. 



