TROOST *S CRINOIDS OF TENNESSEE — E. WOOD. 101 



increases also, notwithstanding the plates continue of the same size; but we find some 

 of them changed, having then a cuneiform summit, which admits some additional 

 plates in the following rows. These cuneiform or pentagonal plates seem to be irreg- 

 ularly dispersed over the body. The surface of the plates is slightly convex, and 

 radiating striae run from the centre towards the sides. 



This is the only character which distinguishes these plates from those of the Melonites 

 which are granulated. 



Nothing is known of its superior part as appears from the figure — I conjecture from 

 some appearances that it terminated in an uniform margin. 



I found it on the bank of Duck River near Columbia, Maury ( iounty, Tenn. The same 

 Silurian as the vicinity of Nashville. 



Observations. — As shown by the figure, only a portion of the calyx 

 of this specimen is preserved, but the arrangement of the plates, their 

 striated surfaces and crenulated sutures place it in the genus Cleio- 

 crinus. The radiating ridges mentioned by Troost appear on plates 

 preserving the outer surface but where this is removed the plates are 

 crossed longitudinally by fine grooves which probably formed chan- 

 nels within the substance of the plates. These are continuous across 

 adjacent plates. 



The species is most nearly related to ('. magnificus Billings, but it 

 differs in the form of the body which was apparently more slender, 

 and in the shape of the plates which are longer and narrower than in 

 C. magnificus. 



Formation and locality. — Lebanon limestone division of the Stones 

 River formation. Duck River, near Columbia, Maury County, 

 Tennessee. 



Cat, Xo. 39910, U.S.X.M. 



Order DICYCLICA CAMERATA Bather. 



Family DIMEROCRIXID^. 



Genus DIMEROCRINUS Phillips. 



DIMEROCRINUS ROEMERI (Troost). 

 Plate 15, fig. 4. 

 Gilbertsocrinites roemeri Troost, MSS., 1850. 

 The original description by Troost is as follows : 



It is inverted conical. The column is cylindrical with a pentapetalous alimentary 

 canal [lumen]. The plates are slightly tumoue. The live arms are divided into ten 

 hands before they reach the rim of the cup. 



Decatur County, Tennessee. 



Supplementary description. — Calyx obconical; height to the arm 

 bases 12 mm.; greatest diameter 15 mm. 



Infrabasals five, small, only their superior angles projecting beyond 

 the column; basals large, thier lower portions slightly nodose; radiais 

 the largest plates of the calyx; first primibrachs with a variable number 



