TROOST 7 S CRINOIDS OF TENNESSEE E. WOOD. 



89 



a point at the center of the base, but the posterior infrabasal is 

 smaller and does not quite reach the center. 



If the discovery of other stemless individuals of this species should 

 show the absence of a column to be a constant feature they would 

 constitute a new genus, since they differ in the respects enumerated 

 above from the stemless genus Agassizocrinus , but pending such dis- 

 covery the single specimen at hand is placed with the genus Scytalo- 

 crinus, to which it is evidently closely related. 



This species is distinguished from 8. decabrachiatus Hall, its nearest 

 ally, by the proportionally larger infrabasals, hexagonal instead of 

 pentagonal basals, and by the strong median constriction of the 

 primaxils. 



The plates of the large central sac are well shown. The margins 

 are cut into slender fringes by the elongate slit-like pores which cross 

 the suture lines between them. 



Formation and locality. — St. Louis limestone. Huntsville, Ala- 

 bama. 



Cat. No. 39917, U.S.N.M. 



Genus ZEACRINUS Troost. 



Zeacrinites Troost, Proc. Amer. Ass. Adv. Sci., II (read 1849), 1850, p. 61 (nomen 

 nudum); MSS., 1850. 



Zeacrinus Hall, Geol. Surv. Iowa, I, Pt. 2, 1858, p. 544. — Meek and Worthen, 

 Geol. Rep. Illinois, II, 1860, p. 186. — Shumard, Trans. Acad. Sci. St. Louis, 

 II, No. 2, 1866, p. 398. — Wachsmuth and Springer, Rev. Palseocrinoidea, I, 

 1879, p. 125.— Miller, North Amer. Geol. and Pal., 1889, p. 288.— Zittel, 

 Text-Book Pal. (Eastman trans.), 1896, p. 160. — Bather, A Treatise on 

 Zoology, III, The Echinoderma, 1900, p. 180. 



The original description by Troost is as follows : 



If the number of plates that compose the body of an Encrinite determine its genus, 

 then the one under consideration must perhaps be placed in that of the Cyathocrinites, 

 but if the arrangement of these plates is also necessary to determine its genus then 

 this crinoid can not belong to the Cythocrinites and forms a new genus, to which I have 

 applied the name of Zeacrinites. a 



Observations. — Doctor Troost's remarks, together with a detailed 

 description and diagram of plates, were published by Hall (1858, 

 p. 544). 



a Zeacrinites from Zea — maize — one of my negro servants, being present when I found 

 this specimen — "Ah! Masse " (he said) "a petrified corn cob "! — in fact it resembles as 

 much a corn cob, as an Apiocrinus resembles a pear or a Rhodocrinus a rose.— So I am 

 indebted for the name of this fossil to a descendant of an African race. I gave it only a 

 scientific appearance, to which I have joined the name of another plant which adorns 

 our western forests by the beauty of its flowers and delicacy of its perfume namely the 

 magnolia, by which I was surrounded when I found it. 



