688 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



circular, occupying one third the width of the plates. Costals subtrigonal, 

 the sloping upper faces concave, and their angle rather sharp. Distichals 

 and palmars once and a half as wide as long. Arms from sis to eight to the 

 ray, of nearly uniform size throughout, biserial from their fourth or fifth 

 plate ; the joints moderately long, united by slightly waving sutures. Pin- 

 nules strong, composed of long joints. Structure of ventral disk unknown. 



Horizon and LocalUi/. — Upper Burhngton hmestone, Burlington, Iowa. 



T//pe in the Museum of Comparative Zoology. 



Eemarks. — In this species Meek and Worthen included another form, 

 which we have described under the name of PMi/crinus nodostriatus, and 

 which differs essentially in the form of the basal cup, and in the style 

 of ornamentation. 



Platycrinus brevinodus Hall. 



FMe LXX. Figs. %, 5, 6a, b. 



1861. Hall; Descr. New Spnc. Crin. p. i, and Bost. Journ. Nat. Hist., p. 286; figured 1872, N. Y. State 



Museum, Bull. 1, Plate %A, Fig. 5. 

 1881. W. and Sp. ; Revision, Part II., p. 70 (Proceed. Acad. Nat. Sci. PhUa., p. 244). 



A rather small species. Dorsal cup nearly twice as wide as high, slightly 

 spreading, broadly truncate at the base. Basals proportionally large, disk- 

 like, truncate below, onlj' the extreme upper ends turning upwards, very 

 little concave, and the outer margins surrounded by a row of conspicuous 

 nodes, directed outward and giving to the edges a crenulated outline ; the 

 interbasal sutures obsolete. Radials wider than long, a little widest at the 

 top; subquadrangular; the outer ends of the upper face but slightly sloping, 

 except those of the anal side, which form a distinct notch, and support a 

 rather large hexagonal plate. Radial facets shallow, occupying half the 

 width of the plates. Basi-radial and interradial suture lines grooved. Cos- 

 tals triangular, moderately large, occupying the whole width of the facets. 

 Distichals two, free from the costals up, the first once and a half as wide as 

 long ; the second as long as wide. Palmars, when present, but little larger 

 than the succeeding arm plates. Arms four to six to the ray in the same 

 specimen, rather slender and tapering ; their proximal ends composed of five 

 to six cuneiform pieces, which gradually turn into biserial above. Pinnules 

 placed somewhat distant. Structure of ventral disk unknown. 



Horizon and Locality. — Described from the Keokuk group at Keokuk, 

 Iowa; but occurring also at the same horizon at Indian creek, Montgomery 

 Co., Ind., and in the Burlington and Keokuk transition beds near Burlington. 



