602 THE CRINOIDEA CAIIERATA OF NORTH AMERICA. 



than long. First costals larger than the second, quadrangular or pentangular; 

 the second pentangular or heptangular. Distichals one, axillary, supporting 

 within the calyx two single palmars, followed by the free arm plates, which 

 from the second piece are arranged in double rows. Arms crowded, long and 

 heavy ; their upper ends rapidly tapering to a fine point ; the plates some- 

 what transversely angular, and the suture lines parallel. Pinnules in close 

 contact, composed of about fifteen joints, from two and a half to three times 

 as long as wide ; all, with the exception of the three upper ones, provided 

 with a prominent, sharp hook, directed obliquely upward, and arranged 

 longitudinally in rows parallel with the sides of the arms. Regular inter- 

 brachials : 1, 2, 1 ; large specimens have an additional row of two plates, 

 and the second palmars take part in the calyx ; the palmars of adjacent 

 rays in contact laterally. The first anal plate is followed by three to five 

 interbrachials, there being no higher anals, and the species has no interdis- 

 tichals. Ventral disk conical, composed of rather large, spinous or nodose 

 plates, separated by small, convex pieces. The plates are irregularly 

 arranged, and the orals and radial dome plates are with difficulty recog- 

 nized ; the posterior oral is erect, and forms a part of the anal tube. The 

 tube, which extends considerably beyond the limits of the arms, is composed 

 of convex pieces ; it tapers gradually, arid is quite slender at the upper 

 end. Column strong, composed near the calyx of alternate thick and thin 

 joints with rounded edges ; the former increase in diameter downwards, 

 while the latter grow narrower, gradually become cylindrical, and increase 

 in number quite rapidly, there being already seven to the internode at 

 90 mm. from the calyx. 



Horizon and Locality. — One of the characteristic fossils of the Lower 

 Burlington limestone; Burlington, Iowa, Sedalia, Mo., and Lake Valley, 

 New Mexico. 



Eemarlis. — "We regard Hall's Adinocrinus qudernarius and its variety 

 spini/erus, his A. excerptvs, A. ihemis, and A. lagena, as mere variations of this 

 species, differing slightly in the matter of ornamentation. They cannot be 

 separated in large collections, although they may seem to be quite distinct 

 in individual specimens. Our study of the species is based upon over one 

 hundred good specimens. 



