PALEONTOLOGY OF IOWA. 

 Fio.91. 



609 



The above diagram illustrates the structure, from the specimen figured on Plate 

 xv, fig. 3. The left antero-lateral ray is the only one where the plates are preserved 

 to the bases of the arms. Fig. 1 represents the upper articulating surfaces of the 

 third radial plates, showing the broad area for the reception of the succeeding plates. 



Geological formation and locality. In the Keokuk limestone : Warsaw, 

 Illinois. 



Actinocrinus nashvill&e. 



PLATE XV. FIG. 4; and PLATE XVI. FIG. 4 a, b. 



Actinocrinus nashvillce : TROOST, Monograph of Crinoidese, MS. ; Catalogue of Crinoideae, 

 Proceedings of Am. Association for the Advancement of Science, 1849, p. 60. 



BODY urnshaped, rounded at base and excavated for the 

 reception of the column, contracted above, and somewhat 

 rapidly expanding at the brachial margin : dome moderately 

 elevated, with a strong central proboscis. Basal plates more 

 than twice as wide as long, spreading in a broad thickened 

 rim, indented at the line of suture . First radial plates large, 

 wider than long, tuberculose transversely, and prominent 

 [lowA SURVEY.] 77 



