Summit Structure of Pentremites. 505 



Column ratlicr yniall, round, and composed of lliin 

 joints, alternating in size. 



This species has an appearance quite unlike any other 

 with which it is associated. 



Locality and position in the upper division of the Bur- 

 lington Tiimestone, Burlington, Iowa. 



Collection of Rev. W. H. Barris. 



Genus SCAPHIOCRINUS Hall. 



Scaphiocrirms rusticellus (n. s.) Body moderately small ; 

 base comparatively broad, full half as broad as the top of 

 the calyx ; rather deep depressions at the suture angles of 

 the body plates, except those at the lower angles of the 

 subradials, at the junction of the basal plates. At a point 

 on the column about as far below the base as the height 

 of the calyx^ there is a joint wider than the others, below 

 which the column is roughly pentangular, and above which 

 it is pentalobate, and increases so rapidly in size to the 

 base that the sides of the calyx and the column are nearly 

 on a line with each other. The lobes of each part of the 

 column continue up to, and include the subradials, the 

 depressions between them ending at the lower ends of the 

 first radials. The column is composed of thin joints alter- 

 nating in size so as to give the lobes a nodose appearance. 

 Basal plates moderately large, appearing beyond the col- 

 umn in subtriangular, excavated faces ; subradials of mod- 

 erate size, the sides being very short, gives them a sub- 

 quadrangular appearance ; first radials larger than the 

 subradials, a little wider than high, having depressed sut- 

 ures between them ; second radials larger than the first, a 

 little higher than wide, except the anterior one, which is a 

 little shorter than the others ; these are rather robust, and 

 a little constricted just below their upper ends. These 

 support two arms each, but the condition of our specimen 



JOUKNAL B. S. N. H. 64 JANUARY, 18C3. 



