ACTINOCEINID^. 609 



the plates of one series stand obliquely to those of the opposite one, the 

 outer ends of the plates directed slightly downward. Each plate, close to 

 the upper margin, is marked by a sharp, conspicuous transverse ridge, while 

 the lower parts of the plates are beautifully corrugated. The transverse 

 ridges, -which somewhat resemble the teeth of a file, suggested the specific 

 name. Pinnules long ; the dorsal side of each joint armed with a sharp, 

 curved spine. Eegular interbrachials : 1, 2, 2. Anal plate followed by 

 2, 2, 2 plates, and these by two very minute pieces, placed within the arm 

 regions. Interdistichals one, large. Ventral disk depressed conical, com- 

 posed of comparatively few large plates, the centre of which is produced 

 into a small slender spine. Anal tube moderately large, and almost 

 central. 



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



I't/pe in the University Museum at Ann Arbor. 



Remarks. — Differing from all other Burlington species of this genus in 

 the surface markings of the arms. The set of arms figured by Whitfield 

 (Mem. Am. Mus. Nat. Hist. N. York, Plate 1, figs. 8 and 9) as of this species, 

 in our opinion belongs to Actinocrimis tenm'scidptiis McChesney ; they do not 

 show the sharp file-like ridge of each joint, which is so characteristic of this 

 species. 



Cactocrinus longUS (Meek and Woethen). 



Plate LVII. Fig. 8. 



1869. Adinoerinus longus — Meek and Wokiben; Proceed. Acad. Nat. Sci. Pbila., p. 156. 



1873. Actimorinus lonr/us — Meek andWoKTHEN; Geol. Rep. Illinois, Vol. V., p. 345, Plate 8, 



Pigs. \a, b. 

 1881. Aclinocrinus longus — W. and Sp. ; Revision Palseocr., Part II., p. 144. 



A large and elongate species. Calyx to the base of the anal tube 

 almost once and a half as high as wide. Dorsal cup somewhat shorter than 

 its width across the arm bases, the sides a little convex. Plates rather 

 thin, very slightly elevated, and in well preserved specimens ornamented 

 with very fine, more or less obiscure ridges, which in sets of from one to five 

 pass from plate to plate. The basals, radials, and costals are traversed by 

 five such ridges ; five others proceed to adjoining radials and the anal plate, 

 but only three from the costals and radials to the lower interbrachials, and 

 from the costals to the distichals, while all the remaining plates have single 

 ridges. The suture lines, except the basi-radial and interradial ones, rarely 

 observed. 



77 



