480 THE CEINOIDEA CAMERATA OF NORTH AJIERICA. 



Aorocrinus elegans (S. A. Millee). 

 Plate XXXIV. Figs. 17a, h. 



1892. Dorycrinus eleffiiM — S. A.Miller; Adv. Sheets IStli Rep. Geol. Suit. Indiana, p. 17, Plate 3, 

 rigs, i aud 5. 



A moderately small species, calyx obconoidal, as wide as high, the base 

 truncated, the sides almost straight, and not grooved between the rays, 

 except the anal side which has a depression at the arm regions. The 

 plates slightly convex but without ornamentation ; the suture lines some- 

 what channeled. 



Basal cup rather high, subcylindrical, the interbasal sutures slightly 

 notched at the bottom; the column facet deeply depressed, and occupying 

 half the diameter of the cup at the lower end. Eadials a little spreading, 

 larger than both costals together, and generally as long as wide, their lateral 

 faces longer than the upper. Costals small, variable in form and size, some of 

 them quite narrow and ahnost as long as wide, others almost twice as wide as 

 long ; the first quadrangular, the second pentangular, hexangular or heptan- 

 gular, owing to the height of the adjoining first interbrachial. Distichals two, 

 as large as the costals and of similar form. Palmars but one row in the 

 calyx. Arms four to the ray ; their structure not observed, but they evi- 

 dently were simple, to judge from the arm openings. Eegular interbrachi- 

 als three ; the first rather large, and about as high as wide ; the two of the 

 second row less than half the size of the first, and one of them generally 

 a little larger than the other, both separated from the plates of the disk 

 by the palmars, which meet above. Anal plate of the size of the radials ; 

 followed by three plates, which are almost as large as the first interbrachial 

 of the regular sides. There are three smaller plates in the third row, and 

 these are succeeded by a very large elongate plate, which forms the bottom 

 of the depre.ssion at the arm regions. Ventral disk very slightly convex, 

 almost flat, and composed of but few large plates. The orals decidedly 

 asymmetrical in their arrangement, the two postero-lateral ones forming 

 a straight line with the posterior one ; they are very large and occupy 

 almost one half of the disk. The ambulacra represented by one large plate, 

 followed by two somewhat smaller ones of a secondary order. The inter- 

 ambulacral plates consist of only two very narrow, elongate pieces. Anus 

 subcentral, in close proximity to the posterior oral, directed upwards, and 

 placed in the centre of a short protuberance. 



