324 PROCEEDINGS OF THE ACADEMY OF [1879. 



and short, articulating face circular ; the first one extremely short 

 in the middle, one fourth as high as wide, and becoming still thin- 

 ner or wedge-shaped at each side ; the second is a little longer in 

 proportion and presents a subtrigonal outline, supporting on its 

 sloping upper sides two arms. 



Arms moderately long, robust, scarcely decreasing in size, and 

 generally simple throughout, though sometimes they branch once 

 on the third or fourth plate in some of the rays but never in 

 the anterior one and only in one arm to a ray, the other arm 

 always remaining simple. In one species, probably B. tumidus 

 Hall, from the Keokuk limestone, the antero-lateral raj's are en- 

 tirely simple, the arm plates and brachials forming a continuous 

 series. All the main arms, instead of bifurcating, give off at 

 regular intervals, alternately on opposite sides, and from the inner 

 margins of the plates, short, rounded, simple armlets, which in 

 most species throw off secondary branches as in Botryocrinus, and 

 these armlets, here as there, probably performed the office of pin- 

 nulse. The arm joints are simple, round, mostly shorter than 

 wide, with a narrow, almost linear ambulacral furrow. 



Anal plates generally two, never more. The lower plate which 

 is often very small is wanting in some few species, and in very 

 young specimens is frequently undeveloped, but when present, it 

 is located against the posterior basal and beneath the right radial ; 

 the larger, which stands in line with the radial, is generally of 

 about their height and half their width, quadrangular in outline. 

 Ventral sac and vault unknown, but both were evidently of a 

 delicate structure, as we have never seen a trace of them in an}^ of 

 our specimens. 



Column short, obtusely pentagonal, divided longitudinally into 

 five sections, which are in a radial position. The sutures are in- 

 terradial, the opposite of Heterocrinus in which the} r are radial; 

 they are bordered by little pores which apparently communicated 

 with the lai'ge pentangular central canal at its five angles. These 

 sutures extend throughout the entire length of the stem and partly 

 to the radicular cyrrhi, which are strong, ramifying, and radially 

 situated. The genus had evidently no cyrrhi along the column, 

 for we have examined with reference to this point a number of 

 specimens showing several feet of stem from near the body to, and 

 including the root, without discovering any trace of them. The 

 radicular cirrhi, which are long and strong, are given off radially. 



