ACTINOCEINIDiE. 631 



the second still smaller, being considerably shorter. The size of the distich- 

 als is but little less than that of the upper costals, but the plates of the suc- 

 ceeding orders are considerably smaller. There are five bifurcations in each 

 main division of the ray, and six arms, or twelve to the ray. Arms moder- 

 ately long, much larger than those of the preceding species, laterally com- 

 pressed at their lower ends, and distinctly angular on the back throughout. 

 The arm joints are transversely angular, and have a small elevation or 

 sharp node at each end, giving to the section of the arm a trigonal outline. 

 Pinnules provided with long hooks, similar to those of Cactocrinus. Inter- 

 brachials : 1,2,2,21 ; the latter on a level with the distichals, and quite 

 small ; the first as large as the first costals, or larger. Anal plate as large 

 as the radials, followed by 2, 3, and about 6 irregularly arranged plates above, 

 "which are roofed by the palmars. Interdistichals one. Tegmen moderately 

 convex, slightly plicated near the outer margins, and composed of large 

 plates scattered among smaller ones. The sutures between the plates dis- 

 tinctly grooved, but the surface flat, and covered with wrinkles, which give 

 it a decidedly granular appearance. Anal tube central, long, rather large 

 around the base, but decreasing rapidly to two thirds its largest size, and 

 then tapering slightly to the end. The tube consists of short, very wide 

 pieces, arranged in transverse rows, and covered with wrinkles like those of 

 the tegmen. It is surrounded at half way to the margin of the disk by an 

 irregular ring of ten to fifteen large, spinous plates, which sometimes 

 bifurcate, and rise to a height of from 40 to 80 mm. It is barely possible 

 that these plates represent the orals and radial dome plates, or the latter 

 only, but if so their arrangement is very irregular. Column beautifully 

 sculptured with six rows of large angular processes, longitudinally arranged, 

 ■which give to the stem a distinctly hexangular outline. 



Horizon and Locality. — Lower part of U^jper Burlington limestone, 

 Burlington, Iowa. 



Tt/i}e in the (Worthen) Illinois State collection, Springfield. 



Remarks. — This species is most nearly related to Teldocriniis mnhroms 

 Hall, but differs in never having more than twelve arms, even in the largest 

 specimens; besides the arms are much stronger, and angular on the back 

 instead of flattened. It also difiers in the shape of the rim, and the aspect of 

 the ventral disk, its wrinkled surface, as well as the long spines ; and it is 

 very distinct in the sculpturing of the column. 



Comparison with the types shows that Actinocrinus clivosvs, A. erodus, 

 and A. inscuJ^itJis, all described by Hall, are synonymous with this species. 



