136 PROCEEDINGS OF THE ACADEMY OF [1886. 



Arms long ; bifurcating at regular intervals ; widely divergent, 

 rather stout at their origin ; tapering upward. They are composed 

 of a succession of rather long, quadrangular pieces, interrupted 

 only by the axillaries which are pentangular, and which divide 

 the main arm, and each division of the arm, into two equal parts. 

 The pinnules are slender, composed of long pieces, given off from 

 every arm joint, but at one side only in succession not alter- 

 nately until the next bifurcation of the arm, when on both 

 divisions they all change to the opposite side. By this an-ange- 

 ment there are always 8 to 10 pinnules in succession, first on one 

 side, then on the other. The first pinnule occurs on the second 

 arm plate, not on the first, but every succeeding plate is pinnu- 

 lated with the exception of the bifurcating ones. The proximal 

 pinnule after each bifurcation is considerably heavier and longer, 

 almost arm-like, and bifurcating, the others are simple. The arm 

 furrows are shallow but wide, only one side having sockets for 

 the reception of pinnules.^ 



The ventral sac is tubular, and rests upon the left side of the 

 posterior radial as in the Heterocrinidse. The proximal plate of 

 the tube is large, subquadrangular, and is succeeded by other 

 apparently large pieces. Of the plates at the ventral side little 

 is known. S. A. Miller mentions two rows of small pieces near 

 the ventral tube, but, as nothing is known as to their arrangement, 

 they may be covering plates. 



Column very large, almost circular, pentapartite, highly orna- 

 mented ; central canal large, star-shaped, the projections located 

 interradially. The structure of the column along the axial canal 

 resembles that of Barycrinus and Vasocrinus, with which 

 Anomalocrinus agrees also in the form of the calyx. 



Geological Position^ etc. Lower Silurian of America. The 

 only known species are : Anomalocrinus caponi/ormis Lyon, and 

 A. incurvus Meek and Worthen, which have been previously 

 noted. 



Family XX. BELEMNOCRINID^ S. A. Miller. 



S. A. Miller has proposed for the genus Belemnocrinus a 

 separate family, in which we fully agree. It cannot be placed in 

 any of the other groups, without depriving them of their best 

 distinctive characters. It forms a link between Heterocrinidse 



1 Our descriptions of arms and pinnules in this interesting genus were 

 made from a most beautiful specimen in the collection of J. H. Harris, Esq., 

 of Waynesville, O., who had the kindness to send it to us for description. 



