G98 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



from the arm bases to the lower angles of the radials, where they meet with 

 other ridges radiating from the column facet, with which together they form 

 well defined rhombs. Similar ridges proceed horizontally from the radial 

 facets to the sides of the plates, constituting a ring around the upper end of 

 the cup. Each rhomb encloses about twelve prominent, densely arranged 

 nodes, and other nodes fill the triang-ular spaces between the rhombs. Basi- 

 radial and interradial suture lines not grooved, the interbasal ones obsolete. 



Basal cup broadly obconical, its height equal to half the length of the 

 radials ; the column facet narrow. Radials slightly spreading, subquadrangu- 

 lar, three fourths as long as wide ; the lower face equal to the lateral ones ; 

 the limbs at the sides of the facets a little sloping, supporting a very large 

 interradial plate ; the facets extremely small, occupying less than one fourth 

 the width of the plates, and entering but slightly the upper margins. Cos- 

 tals pentangular, as long as wide, sharply angular at the to]) : the distichals 

 as long, but a little narrower. Arms four to six to the ray, quite delicate, and 

 composed of long, cuneate pieces which gradually interlock. The brachials, 

 from the radials up, provided with well defined .sharp projections at both the 

 upper and lower ends; the middle portions deeply constricted, producing a 

 somewhat zigzag appearance ; the lines of union rather gaping. Pinnules 

 moderately strong, and not in contact. The ventral disk is covered by the 

 arms in the two specimens examined, with the exception of the interradials 

 of the first row, the middle one of which is proportionally large and covered 

 with nodes similar to those upon the radials, the two at the sides being nar- 

 row and without ornamentation. Proximal stem joints circular, with small 

 nodes surrounding their margins. 



Horizon and Locality. — Upper Burlington limestone ; Burlington, Iowa. 



Tyj^es in the Museum of Comparative Zoology. 



Platycrinus nodo-striatus W. and Sp. (nov. spec). 

 Plate LXVI. Figs. 5a, i ; Plate LXX. Figs. 3, 4a, h, c. 



Of medium size. Calyx globular, about as wide as high, rounded at both 

 ends. Width of dorsal ciTp once and a half to twice its length, the entire 

 surface of the plates densely covered with more or less confluent nodes, 

 arranged in concentric lines around their margins, and traversed by two well 

 defined ridges or rows of nodes passing out from the facets to the lower 

 angles of the plates. The nodes surrounding the column facet more promi- 



