PALEONTOLOGY OF IOWA. 615 



Actinocrinus ramulosus (n.s.). 



PLATE XV. FIG. 7. 



BODY depressed-urnform : base moderately depressed in 

 the centre for the attachment of the column. Basal plates 

 short, expanded below and spreading in a broad rim beyond 

 the column, slightly grooved at the sutures. First radial 

 plates much wider than long, with a transverse angular ridge 

 in the centre. Second radials short, quadrangular, nearly 

 twice as wide as long, each with a central node or tubercle. 

 Third radials pentangular, with a bifurcating ridge on each 

 plate, which diverges to the upper sloping margins, from 

 each of which proceed in succession a quadrangular and a 

 pentagonal supraradial ; from the latter of which proceed 

 two series of three or four brachial plates each, to the base 

 of the arms. The surface of all these plates, from the third 

 radial, is marked by a strong longitudinal ridge, which bi- 

 furcates on the pentangular supraradial ; thus giving origin 

 to four arms from each ray, the number being apparently 

 uniform throughout. First interradial plate large, ten-sided, 

 resting on the two first radials, and supported on each side 

 by the second and third radials and first supraradials, and 

 supporting two second interradials which sustain in part the 

 supraradial plates. Anal plates undetermined. Summit com- 

 posed of numerous tuberculiform plates, without proboscis? 



This species is distinguished from all the other forms here described, by the mode 

 of bifurcation of the radial plates, the strong ridges marking the surface of the 

 third radial, and the plates above continuing to the base of the arms; giving the 

 appearance of bifurcating branches upon the surface of the body. 



Fig 7. View of a distorted specimen, showing the base and three of the rays. 



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

 Illinois. 



