580 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



other from the opposite. The second distichals are cuneate, so that the 

 sloping upper faces of both together serve as an axihary, from which 

 are given off the free arm trmiks. Each succeeding order of brachials in 

 these branches consists of a single plate, which in form and size resembles 

 the arm-bearing distichals, and each one is irregularly axillary, supporting 

 upon its shorter sloping side an arm, upon the longer upper side a brachial 

 of a higher order. The exact number of successive bifurcations cannot be 

 ascertained, but there were not less than forty from each appendage in full 

 grown specimens. The upper and lower faces of the brachials are parallel, 

 their dorsal or outer surfaces somewhat convex or transversely angular. The 

 trunks are nearly three times as thick as the arms, and taper but slightly. 

 Their inner cavity, which is oval in outline, is roofed over ventrally by two 

 series of side pieces, which enclose a row of large, distinctly cuneate covei-- 

 ing plates, alternately arranged, and extended into long, upright spines. 

 The apposed faces of the lower brachials, from the costals up, have a perfo- 

 rate transverse ridge, and the facets of the proximal arm joints also are per- 

 forated, but have in place of a ridge a concave surface. From the rigid ventral 

 structure of these appendages, it seems impossible that there could have 

 been any mobility between the brachials, but there was evidently some sort 

 of articulation at the base of the arms. Arms very short and of equal length. 

 They are given off at almost right angles, are biserial, somewhat flattened, 

 and every arm joint on either side is produced laterally into a prominent 

 spine. At the side of each ai'm, close to the base, there is a small respiratory 

 pore. First interbrachials larger than the first costals, followed by four plates, 

 which are placed on a level with the arm trunks, the two outer ones, which 

 are somewhat smaller, being in part interambulacral ; they bend outward, 

 and help to form the trunks. The anal plate is smaller than the radials, and 

 supports two plates in the first row and five in the second, the latter arranged 

 like the corresponding plates of the regular sides. Tegmen depressed, sur- 

 mounted by a moderately large anal tube, rising abruptly from the summit ; 

 the plates are large, almost flat, and either perfectly smooth, or crowned by 

 a small central tubercle. Orals in lateral contact ; the posterior one unusu- 

 ally small and lunate, its place being largely taken up by the tube. The 

 ambulacral plates elevated, alternately arranged in two rows; the axillary 

 plate spinous. The plates of the anal tube strongly nodose. 



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

 Sedalia, Mo., and Lake Valley, New Mexico. 



