PALAEONTOLOGY OF IOWA. 619 



towards the summit, the anterior range terminating as usual 

 in the Actinocrinus in two such plates ; the summit crowned 

 by a larger tuberculiforrn plate. Entire surface granulate or 

 granulose striate towards the margins of the plates. 



Fig. 2 a. The anal side of a specimen from which the arms have been separated. 



Fig. 2 b. The base of the same specimen, the basal plates not being visible beyond the 



circumference of the column. All the other plates, to the base of the arms, 



are shown in this figure. 

 Fig. 2 c. The dome, showing the aperture which opens upwards, the central tuberculi- 



form plate, and the ranges of larger plates from each arm; there being two 



in the range of the anterior arm, at the base of the central plate. 



Geological formation and localities. In the Keokuk limestone : Keokuk, 

 Iowa ; Nauvoo and Warsaw, Illinois ; White's Creek springs, Tennessee. 

 The latter locality is that cited by Dr. TROOST, and the specimens from 

 that place show no specific difference from those of the more northern lo- 

 calities. 



Agaricocrinus wortlieni ( n. s.). 



PLATE XVI. Fm. 1. 



BODY robust, somewhat hemispheric : base concave, the 

 concavity extending to the base or middle of the third ra- 

 dial plate. Basal plates nearly hidden by the column. First 

 radial plates wider than long, hexagonal. Second radials 

 hexagonal, the upper angles being truncated by the second 

 interradial plates. Third radials strong, pentagonal ; the sides 

 resting against the second interradial plates, and supporting 

 on their upper sloping faces two strong brachial plates; and 

 these, two other shorter brachials, from which proceed the 

 strong arms, consisting of a double series of very short wide 

 plates which are abruptly wedgeform at their junction. Arms 

 long, consisting of ninety or more joints in each series : 

 tentacula unknown. 



Interradial plates three : the first one short, hexagonal, 

 supporting two extremely narrow elongate plates ; the latter 

 resting on the sloping upper sides of the first interradial and 

 the truncated upper angle of the second radial plate, resting 

 against the lower lateral margin of the third radial plate, 

 and reaching as high as or higher than the first brachial 



