288 New Species of Crinoidea from the 



plate, and is of an elongate, horseshoe form, broadest at 

 the lower end, with a slightly elevated border around the 

 lower margin; it is occupied by the clavate sub-brachial 

 plate and the outer ends of the first arm plates. 



Arms bifurcating on the sub-brachial plate, each main 

 division again dividing on the second plate above, the in- 

 ner branch again dividing on the succeeding second plate, 

 and the middle branch again dividing on the second plate 

 above the last, giving fom* arms to each main division 

 and eight to the ray. The arms are elongate fusiform, 

 composed of a double series of very short plates, wedge- 

 form at the interlocking edges. Surface of arms marked 

 by fine, interrupted, longitudinal striae, visible only on 

 well-preserved specimens. Surface of body plates covered 

 by short, confluent, setiform spines, which sometimes form 

 lines parallel to the sides of the plate ; in some individu- 

 als these spines are less developed. Suture lines distinct 

 and impressed. 



This species is closely related to P. Shumardianus, (Iowa 

 Geol. Rep. pi. 8, fig. 5;) it differs in the narrower radial 

 plate, and in having two more arms to each ray. 



Geological formation and localiiy. Burlington lime- 

 stone, Burlington, Iowa. Collections of Dr. O. Thieme 

 and of C. A. White. 



GENUS DICIIOCRINUS, Muxstek. 



Dichocrinus plicatus (n. s.). Calyx globular, the great- 

 est diameter through the radial plates at one third above 

 their lower margin. The basal plates form nearly one 

 half the entire height of the cup ; their upper margins 

 strongly undulated for the reception of the radial plates. 

 Radial plates sub-quadrangular, unequal in size, wider at 

 the lower margin, which is marked by a small, shallow 

 scar for the reception of the sub-brachial plate. The anal 

 plate dillers from the radials in being narrower at the top. 



