392 THE CRINOIDEA CAMEEATA OF NORTH AIVIERICA. 



rather deeply concave, directed outward. Auibulacral openings arranged in 

 groups, tlie spaces between the posterior rajs wider than those between the 

 other rays. Respiratory pores large, arranged in five pairs interradial in 

 position. Arms twelve to fourteen, incurving, extremelj' heavy for the size 

 of the species ; they are biserial from the second free plate, rounded on the 

 back in the lower portions, but flat and spatulate above, reaching a width of 

 three times the diameter at the base. In the rounded part, the back of each 

 alternate .plate in both series is covered by a small node, which does not 

 extend to the flattened portions ; the arms are keel-shaped, heavy along the 

 median line, and knife-like at the edges. Interbrachials three to four in the 

 four regular rays; the first large and wider than high; the upper smaller 

 and arched by the arm-bearing brachials. At the posterior side the anal is 

 followed by three and two pieces. The ventral disk consists of but few 

 plates, of which the posterior oral is the largest; it is slightly convex, 

 central in position, and bends upward, forming a part of the ventral tube ; 

 the other orals and radial dome plates are somewhat nodose. Anal tube 

 excentric, large at the base, and curving to one side. 



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



Types in the collection of Wachsmuth and Springer. 



Eretmocrinus depressus w. and Sp. (nov. spec). 

 Plate XXXVI. Figs. 11a, h. 



Near Eretmocrinus remihrachiatus, but the proportions of the cah'x quite 

 different ; the ventral disk comparatively shorter and less bulging ; the bot- 

 tom of the dorsal cup considerably broader, and the arm openings directed 

 obliquely upwards in place of horizontally. The dorsal cup spreads moder- 

 ately from the top of the basals to the top of the distichals, thence abruptly 

 to the arms ; its height is equal to one third its width at the arm bases ; the 

 rays are indistinctly lobed. The plates vary from almost flat to distinctly 

 convex ; they are without ornamentation, and the suture lines are obscure. 



Base extended outward, forming a broad, projecting rim with a sharp 

 edge at the lower border ; its lower face almost flat, and only one third 

 of its width is occupied by the column. Radials comparatively small, a little 

 wider and somewhat longer than the costals ; the latter quadrangular and 

 pentangular. Distichals two, the upper one axillary, giving off from each 

 side two short palmars supporting four arms ; the anterior ray exceptionally 



