TKOOST'S CRINOIDS OF TENNESSEE — E. WOOD. , 



59 



The division of hands and fingers is unknown. 



The capital integument [tegmen] which is large, hemispherical or sometimes pyram- 

 idal, is composed of large tumous plates and terminates at its apex in a still larger 

 hemispherical plate. The whole of its surface seems to have been covered with a 

 finely granulated integument. It had no proboscis, but a prominent oral [anal] 

 aperture, surrounded with numerous small tumous plates, which is placed a little above 

 the junction of the two large arms. 



It is very uncommon to find specimens which exhibit all the characters here enu- 

 merated. The basin shaped concave body, which is composed of the characteristic 

 plates, is generally filled with siliceous matter; in fact, the whole fossil is siliceous. I 

 possess only one specimen (a juvenile one) in which the plates are distinct. 



I discovered only one species of this genus, and only at one locality, namely, near 

 White's Creek Springs, so rich in encrinital remains. 



Observations. — Doctor Troost described under the name of Agarico- 

 crinus tuberosus five species of Agaricocrinus. The description, how- 

 ever, with the exception of the part relating to the number of arms, 

 is evidently taken from a specimen now referred to Agaricocrinus 

 americanus. In this specimen the plates of the calyx are clearly 

 shown, and Troost' s description of them is accurate except in the 

 description of the primibrachs, where he apparently confuses rays in 

 which the first primibrach is abnormally wanting with the normal 

 rays. The specimen is a fourteen armed individual which corre- 

 sponds with the description and figures of Roemer except in the depth 

 of the basal excavation. The latter is much deeper in the specimen 

 at hand than in the one figured by Roemer, but as this feature varies 

 considerably in individuals undoubtedly of the same species it can 

 not be relied upon for specific separation. 



Formation and locality. — Keokuk horizon of the Tullahoma forma- 

 tion. White's Creek Springs, Tennessee. 



Cat. No. 39889, U.S.N.M. 



AGARICOCRINUS ARCULA Miller and Gurley. 



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



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

 Agaricocrinus arcula Miller and Gurley, Bull. No. 6, Illinois State Mus. Nat. 



Hist., 1895, p. 30, pi. in, figs. 7, 8.— Weller, Bull. No. 153, U. S. Geol. 



Surv., 1898, p. 67 (catalogue name). 



Among the specimens described as Agaricocrinus tuberosus Troost 

 (MSS.) is a small ten armed individual which has been referred to A. 

 arcula Miller and Gurley. The chief difference between the specimen 

 and Miller and Gurley's type is that the primaxils and succeeding 

 secundibrachs are slightly convex instead of being flattened. In other 

 respects it agrees closely with the type. 



The tumid plates at the base of the arms form a conspicuous 

 feature of the tegmen. They are nearly or quite as large as the pos- 

 terior oral. 



This species differs from A. tuberosus Hall in the number of arms 

 and from both that species and A. bullatus in the short first inter- 

 brachials which are followed by two relatively broad plates. It is 

 also smaller than A. tuberosus Hall. 



