1886.] NATURAL SCIENCES OF PHILADELPHIA. 167 



ZEACRINUS (Troost MS.) Hall, Rev., i, p. 125. 



Revised W. and Sp. (PI. 6, fig. 9, and PI. 9, fig. 3). 



Zeacrinus differs from Woodocrinus (Pachylocrinus) in the 

 form of the ventral sac, which, as described by us, is pyramidal, 

 sharply angnlar and pointed at the upper end ; while that of 

 Woodocrinus is club-shaped, inflated above. The two genera 

 differ also in the construction and form of the dorsal cup, which 

 in Zeacrinus is much more depressed and disk-like, Basals 

 exceedingly small, trigonal, deeply notched for the reception of 

 the radials. The underbasals at the inner floor of the calyx are 

 generally larger than they appear at the outer side, and the 

 angles of the radials sometimes touch the underbasals. Plates 

 of the calj'x massive, especially the radials, their distal faces 

 sloping outward ; articular facets with muscular extensions. 

 Arm plates generally flat, except the axillaries, which frequently 

 are tuberculous. The arms dichotomize toward the inner side of 

 the ray from each main division, the branches rarely dividing 

 again. The arm joints are short, transversely arranged, those of 

 the same rank slightly increasing in width upwards, those of the 

 next order narrower by one-half than the preceding bifurcating 

 plate. By this structure, the arms. of each ray, and of the main 

 divisions of the rays, form laterally a straight line, by means of 

 which they fit in so closely against the arms of adjoining rays, 

 that thc}^ often appear as if united by suture. Column round, 

 comparatively small. 



We now recognize under Zeacrinus only the following species, 

 viz. : Zeacrinus bifurcatus, Z. compactilis Worthen ; Z. magnolia- 

 formis 0. and N.; .^. ovalis Lyon and Cass.; Z. Wortheni Hall, 

 and our new species Z. nodosus, all other species which were re- 

 ferred bj^ us to this genus are found now under Woodocrinus. 



Zeacrinus nodosus, nov. sp. (PI. 6, fig. ;!). 



The largest known species of the genus. All plates of calyx 

 and arms nodose, except basals and underbasals ; the nodes on 

 , all axillaries, and the first plate of each succeeding order of arm 

 plates, almost covering the entire surface of the plate ; while at 

 the intermediate plates the nodes have more the shape of small 

 tubercles, arranged so as to occupy an excentric position, leaning 

 slightly toward the wider or pinnule-bearing side, thereby forming 

 along the arms two rows of nodes, alternately arranged. 



Underbasals of medium size, extending beyond the column, 



