584 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



almost horizontal ; the former supporthig an arm, which is free from the 

 second plate, the latter two clistichals. The succeeding arms are given off 

 in exactly the same manner as the first ; every second brachial is axillary 

 and supports on its shorter sloping side an arm, and on the opposite side 

 two brachials of a higher order, until finally near the tips of the arms the 

 last axillary gives origin to two arms. In large specimens there are not less 

 than fifty orders of brachials to each ray — a very young specimen before 

 us has but fifteen, and a somewhat larger one twenty-two — and these form 

 straight, arm-like, apparently inflexible trunks, which at the proximal ends 

 are four or five times as heavy as the armlets. The plates of which they are 

 composed are short, three or four times as wide as long, with crenulated 

 apposed faces, the armlets resting against both plates. The inner cavity 

 of the appendages is quite large, suboval in outline, the longer diameter 

 directed dorsally and ventrally,. and the tubes themselves taper but little 

 upward. Their ventral side is roofed by a simple row of large, spinous cov- 

 ering pieces, somewhat wedge-shaped and alternately arranged, together 

 with small, triangular side-pieces, which are united with the brachials and 

 covering plates by close suture. First interbrachial as large as the first 

 costals, the two plates of the second range but very little smaller, those 

 above much smaller and irregularly arranged, varying in the third row from 

 three to five, and in the fourth from five to seven, the latter meeting the 

 tegminal plates. Tegmen high, contracted in the lower part, then rising 

 almost vertically, and rounded near the summit ; it is composed throughout 

 of small, spinous pieces, sharply pointed at the upper end, and so irregular 

 in their ari'angement that neither the orals nor any of the other disk plales 

 can be identified. At one side of each trunk, and always opposite the first 

 arm, within the tegmen, there is a large respiratory pore ; and smaller ones 

 occur along the appendages aside of every arm. Anal tube rather small and 

 nearly central. Column of moderate size, the joints so short that at 30 mm. 

 from the calyx it contains sixty joints with fifteen internodes. The nodal 

 joints very little wider than the intervening ones. 



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

 and Lake Valley, New Mexico. 



Tyjie in the collection of Prof. Worthen. 



Remarks. — This species differs from all others in having but five brachial 

 trunks in place of ten, and in having the lower brachials much more deeply 

 incorporated into the dorsal cup. 



