ACTINOCKINID^. 573 



part of the arm a zigzag outline. The upper parts of the arms have serrated 

 sides, and are comj)osed of two series of moderately long pieces. Regular 

 interbrachials : 1, 2, 2 ; the anal plate followed by 2, 3, and 3 plates. Inter- 

 distichals one, large. Ventral disk not visible in the specimens. 



Horizon and LocaVdij. — Lower Burlington limestone ; Burlington, Iowa. 



Tu'pes in the Museum of Comparative Zoology, and m the collection of 

 Wachsmuth and Springer. 



Actinocrinus tuberculosus W. and Sp. (nov. spec). 

 Plate LII. Figs. 8a, h, c. 



Of the type of A. tenuiscnljjitis, but somewhat larger. Calyx a little 

 higher than wide, the dorsal cup considerably shorter than the tegmen. 

 Plates rather thin, the surface slightly convex, and ornamented by series 

 of isolated nodes of various forms. The middle of the plates is occupied 

 by a conical, sometimes rounded tubercle, which is surrounded by elon- 

 gate nodes, directed one to each side, with their longer diameter toward 

 the margins of the plates. From the middle of the second costals up- 

 ward, sometimes even from the radials, the nodes are set close together 

 in rows, and form high and sharp knife-like ridges with serrated edges, 

 running to the bases of the free arms. 



Basals short, wider at the lower margin than at the upper, at the latter 

 surrounded either by a thickened collar, or by a row of conspicuous nodes, 

 of which there are generally three to each plate. Eadials one third wider 

 than long. First costals half the size of the radials, and quadrangular ; the 

 second a little wider than the first, and heptangular. Distichals and pal- 

 mars keel-shaped ; the former smaller than the costals, and once and a half 

 as wide as long ; the latter still smaller, and the angularity extending over 

 the entire width of the plates. Arms three to each main division of the 

 ray, or thirty in all, given off in the nsual way ; the proximal one from the 

 outer sides of the distichals, the two others from the second palmars ; they 

 are long, flat, wider in the upper part than at their bases ; the lateral mar- 

 gins serrated. The four proximal arm plates are single, very high and cu- 

 neate, a thorn-like projection extending out from their longer sides. The 

 plates, as the arms become biserial, are short, and each one is covered with 

 a transverse row of small pustules. Pinnules long, and to one half their 



