92 BULLETIN 64, UNITED STATES NATIONAL MUSEUM. 



Genus HYDREIONOCRINUS de Koninck. 



HYDREIONOCRINUS DEPRESSUS (Hall). 

 Plate 11, figs. 6, 7, 8. 



Cyathocrinites depressus Troost, Proc. Amer. Ass. Adv. Sci., II (read 1849), 1850, 



p. 61 (nomen nudum); MSS., 1850. 

 Zeacrinus depressus Hall, Rep. Geol. Surv. Iowa, I, Pt. 2, 1858, p. 545, text 



figs. 66, 67. 

 Poleriocrinus (Zeacrinus) depressus Shumard, Trans. Acad. Sci., St. Louis, II, 



No. 3, 1866, p. 362 (catalogue name). 

 Hydreionocrinus depressus Wachsmuth and Springer (not Wetherby), Rev. 



Palseocrinoidea, I, 1879, p. 131 (catalogue name). — Miller, North Amer. 



Geol. and Pal., 1889, p. 256 (catalogue name). — Weller (in part), Bull. No. 



153, U. S. Geol. Surv., 1898, p. 310 (catalogue name). 

 Cyathocrinus depressus Wachsmuth and Springer, Rev. Palseocrinoidea, I, 1879, 



p. 148 (catalogue name). 



The original description by Troost is as follows : 



It differs from the C. crateri/ormis [Eupachycrinus boydi] by being less elevated — 

 but it differs more particularly in the form of the costals [basals] and scapulars [radi- 

 als] — the first shooting up lanceolate along the sides of the cup, while the latter (costals) 

 [radials] being irregularly pentagonal with curvilinear edges fill up the interstices 

 between the costals [basals]. The interscapulars [anal and right tube plate] are regular 

 hexagons. 



It occurs near White's Creek Springs, Davidson County, Tennessee, and in the 

 vicinity of Huntsville, Alabama, both Carboniferous. 



Observations. — In connection with his description of the genus 

 Zeacrinus, Hall has published a brief description of this species, with 

 diagrams of the plates, both exterior and interior views. 



The excellent state of preservation of the dorsal cup of the type- 

 specimen illustrates well the character of the thick plates of which 

 it is formed. The infrabasals have the form of pentagonal prisms, of 

 which the large bases form the inner floor of the calyx, while their 

 truncated apices are the small infrabasals concealed beneath the 

 column on the outside. The basals, which are large and petalloid on 

 the outside, have only their tips showing in the angles between the 

 infrabasals on the inside of the calyx. The long radianal extends 

 downward between the posterior basal and the adjacent radial until 

 its tip truncates that of an infrabasal plate. The special anal and 

 right tube plate are preserved, as shown in the figures. 



The arms, column, and tegmen are unknown, but the species 

 may be referred to Hydreionocrinus on account of the similarity 

 of the calyx to those of undoubted species of the genus. 



Formation and locality. — Chester limestone. Near Huntsville, 

 Alabama. Troost reports the species also from White's Creek 

 Springs, Tennessee, but the four specimens in his collection are 

 evidently all from one locality, and as their method of preserva- 



