370 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



Calj'x somewhat biturbinate, as wide as high. The dorsal cup larger 

 than the ventral disk ; sides expanding gradually to the arm bases and 

 forming nearly a straight line. Plates nodose, except the first costals which 

 are generally flat. 



Base more than twice as wide as high, hexangular as seen from the 

 bottom ; the interbasal suture lines distinctly grooved ; column facet deeply 

 depressed. Eadials wider than long, widest at two thirds their height, exca- 

 vated at the upper edges. Costals small, both together very little more 

 than half the size of the radials ; the first linear ; the second a little longer 

 and wider in the upper part. Disticlials two, excej)t in the divisions facing 

 the anal side, in which there is but one, which is axillary. Palmars 2 X 20 ; 

 but while those approaching the posterior side bifurcate again, the others 

 are followed directly by the free arms. Arm facets concave, arranged in 

 a continuous row around the calyx. Arms twenty-two, short, almost of 

 equal width to their tips. Pinnules closely packed together, long, deep, and 

 flattened at the sides. Regular interbrachials consisting of one large plate, 

 sometimes followed by one or two smaller ones ; the former extending to 

 the top of the first disticlials and even to the palmars. Anal plate consider- 

 ably higher than the radials and succeeded by three large plates, and these 

 by a single one. Ventral disk subconical, plates tuberculose, pointed at the 

 top. Orals and first radial dome plates larger than the intervening supple- 

 mentary pieces, which are quite irregular in form and size. Anal tube very 

 long, sometimes extending several inches beyond the tijjs of the arms ; com- 

 posed of tumid plates. Colunm constructed of rather large joints with 

 rounded edges ; the internodals somewhat the narrowest. 



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

 and in rock of the same age in Southern Missouri. 



Type in the (Worthen) Illinois State collection, Springfield. 



Remarks. — There is not the least doubt that Aetinocrimis diseoideus and 

 A.formosus, both described by Hall, are identical with this species. The 

 former name has priority, but, being described from a crushed specimen, and 

 neither the name nor the description giving a correct idea of the species, we 

 are compelled to adopt McChesney's name. The form described as Aetino- 

 crimis formosiis differs only in the less convexity of the plates. 



