576 ■ THE CEINOIDEA CAMEKATA OF NOETH AMEEICA. 



slightly projecting outward ; axial canal very small. Eadials and anal plate 

 nearly or fully as long as wide. First costals one third smaller than the 

 radials ; the second costals narrower than the first, and smaller generally. 

 Higher brachials gradually decreasing in size upward, each one support- 

 ing an arm at one side, and the upper one two arms. Arms normally 

 eight to the ray ; small, to judge from the size of their facets. Kegular 

 interbrachials : 1, 2, 2, against 2, 3, 2 at the anal side, followed by two 

 very small pieces between the lobes. Interaxillaries one, which, like the 

 interbrachials, meets with the plates of the tegmen. Ventral disk less than 

 one third the height of the calyx, depressed conical, deeply grooved toward 

 the margin. The plates are quite small, scale-like, slightly convex, and of 

 nearly uniform size. Orals indeterminable, but there are along the line of 

 the ambulacra, over each ray, three plates somewhat larger than the others, 

 •which may represent radial dome plates of a first and second order. Anal 

 tube almost central, small for the genus. 



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



Type in the Illinois State Collection at Springfield. 



EemarJcs. — This species, which represents a transition toward Teleio- 

 crinus, is readily distinguished by the depressed form of the disk, and tlie 

 scale-like plates of which it is composed. 



Actinocrinus trijugis (S. A. Miller). 

 Plate LIV. Figs. 4a, h. 



1891. Bhiirocrimis irijmjis — S. A. Miller; Adv. Sheets 17tli Eep. Geol. Surv. ludianaj p, 69, Plate 11, 

 Kgs. 1, 2, 3. 



A small species of the type of A. tenuisculptus. Calyx wider than high, 

 distinctly lobed between the arm bases. Dorsal cup low cup-shaped, about 

 twice as wide as high, the sides rapidly spreading and convex. Surface of 

 plates covered with angular radiating ridges, which meet in a small node at 

 the centre of the plates ; there being one ridge to each side except from the 

 antero-lateral radials and anal plate, whence two ridges pass to the basals. 

 The ridges passing up the radials and brachials somewhat the strongest. 



Basals small, forming an almost flat hexagonal disk, which is but little 

 larger than the column, and has a small, pentangular axial canal. Eadials 

 large, nearly as long as wide. First costals quadrangular, twice as wide as 

 long ; the second a little larger and pentangular. Distichals moderately 



