58 



BULLETIN 64, UNITED STATES NATIONAL MUSEUM. 



Hall considers A. tuberosus Hall and AmpJioracrinus americanus 

 Roemer as possibly synonymous, but they differ in the number of 

 arms and in other important respects as noted by Miller and Gurley 

 [1897, p. 11] and Wachsmuth and Springer [1897, p. 490]. 



AGARICROCRINUS AMERICANUS Roemer. 



Plate 5, fig. 9. 



Agaricocrinus tuberosus Troost (in part), Proc. Amer. Ass. Adv. Sci., II (read 



1849), 1850, p. 60 (nomen nudum); MSS., 1850. 

 Amphoracrinus americanus Roemer, Lethaea Geogn. (3rd ed.), 1855, p. 250, pi.. 



iv, figs. 15a, b. 



Agaricocrinus americanus Shumard, Trans. Acad. Sci. St. Louis, II, No. 2, 1866, 

 p. 351 (catalogue name).— Wachsmuth and Springer, Rev. Palseocrinoidea, 

 II, 1881, p. 228 (catalogue name). — Miller, North Amer. Geol. and Pal., 

 1889, p. 220 (catalogue name).— Gordon, Amer. Geol., V. 1890, p. 261, figs. 

 2-5; Proc. Iowa Acad. Sci., I, Pt. 1, 1890, p. 101.— Keyes, Missouri Geol. 

 Surv., IV, 1894, p. 168, pi. xxn, figs. 8a-b. — Wachsmuth and Springer, 

 North Amer. Crinoidea Camerata, 1897, p. 488, pi. xlii, figs. 1, 2a, b. — 

 Weller, Bull. No. 153, U. S. Geol. Surv., 1898, p. 67 (catalogue name). 



The following description is by Troost: 



The pelvis [base] is concave, bearing a circular impression of a cylindrical column, 

 the articulating surface of which is striated. 



Costals [radials and anal plate], six, hexagonal, placed upon the six sides of the 

 pelvis, forming a hexagon with six re-entering angles. 



Scapulars [first primibraches] five, pentagonal [quadrilateral], placed upon the 

 hexagonal costals [radials]. 



Interscapulars [interbrachials], seven, elongated subhexagonal, six being placed in 

 the re-entering angles of the costals [radials] and one is placed like the scapulars upon 

 one of the hexangular costals [anal plate]. These elongated plates, descending to 

 the border of the basin, surrounding [passing over] it and passing between the arms, 

 terminate at the plates which compose the coronal integument, four of them pass 

 singly between four pair of arms, while the other three, namely, the one which is 

 placed upon the costals [anal plate] and two which are placed in the re-entering angles, 

 pass between a single pair of arms, which are more remote from each other, and ter- 

 minate all three, below two small plates, belonging to those that surround the oral 

 [anal] aperture. 



The five scapulars [first primibrachs] support an equal number of subhexangular [?] 

 arm plates [second primibrachs] each having one re-entering and five salient angles, 

 [?] in the former is inserted the superior angle of the scapulars [first primibarchs]. 

 The arm plate [second primibrach] supports on each bevel a low cuneiform plate upon 

 each bevel of which are placed three or four small plates which support a hand [arm]; 

 the number of these hands [arms] is not uniform. From the two arms, between which 

 pass the three elongated plates above mentioned, we have four hands, while the three 

 other arms have generally only two, sometimes one of them has three hands [arms]. 

 This irregularity seems to be accidental— the arms being probably liable to fracture, 

 were then replaced by new ones, which were smaller and the fingers fewer in number. 

 At other times two hands [arms] are joined together. In the latter case the plates are 

 irregular and the number of hands correspond with that of a single arm. All this 

 irregularity must be attributed to accidents during the life of the animal. The large 

 size nevertheless of the two arms between which project the three elongated plates 

 and between which the oral [anal] aperture is placed seems invariable and they have 

 constantly four hands [arms]. 



