164 PROCEEDINGS OP THE ACADEMY OF [1886. 



In our description of Zeacrinus (Rev. i, p. 125), we stated the 

 difficulty of separating it from Woodocrinus. The only ditfer- 

 ence, there noted, was the folding up and the smaller size of the 

 arms in the former, and upon this distinction almost exclusively 

 we based the separation. We also stated that the calyx in 

 Woodocrinus was generall}' more turbinate, in Zeacrinus de- 

 pressed with concave basal regions, but also to this rule we 

 found exceptions among the species which had been referred 

 to the latter. Equally impracticable would be a separation 

 upon the arm joints, although these vary considerably among 

 the typical species. The arms of Zeacrinus magnoliaformis are 

 dorsally perfectly flat, those of Woodocrinus macrodactylus 

 decidedly rounded, and Hall, Meek, Worthen and White placed 

 under Zeacrinus species with flat, rounded and angular arms. 



The species which we arranged in Pt. i, under Pacht/locrinus, 

 had been originally, with a few exceptions, described under 

 Zeacrinus. Their arms, like those of the latter, are more or less 

 closelj' folded up, and they dichotomize in a similar manner. All 

 are composed of short quadrangular joints, and all have a club- or 

 elongate balloon-shaped, ventral sa<; ; while the sac in Zeacrinus 

 magnoliaformis is pyramidal, with sharp lateral edges and concave 

 sides. In the latter the form of the calyx is disk-like, in the 

 others bowl-shaped. Mr. Percy Sladen, the only English writer 

 who advocated the necessity of subdividing the original genus 

 Poteriocrinus, placed Poteriocrinus 3IcCoi/a7ius, P. calyx, P. 

 granulosus and F. Phillipsii under Zeacrinus. We fully agree 

 with him that these four species cannot be retained under Poterio- 

 crinus, having close affinities with Zeacrinus, but we believe the 

 three former will prove to be Eydreionocrinus, his Zeacrinus 

 Phillipsii a Pachylocrinus or Woodocrinus, as also Poteriocrinus 

 latifrons Austin, which he referred to Scaphiocrinus. Sladen 

 probably was not acquainted with Troost's type of Zeacrinus. as 

 he took Z. elegans to be a typical form, an opinion in which we 

 have shared until quite recently, when we obtained numerous 

 beautifully-preserved specimens, both of "Zeacrinus " elegans and 

 Troost's typical species, from the Kaskaskia limestone. The 

 later- forms differ from the earlier not only in the form of their 

 ventral sac, but also essentially in the construction of their 

 calyx. In the typical species the dorsal cup is disk-like, almost 



