8 BULLETIN 64, UNITED STATES NATIONAL MUSEUM. 



Stereom thrown into strong folds passing from the center of each 

 plate across the sutures to the centers of all adjacent plates, and form- 

 ing prominent triangular figures. On parts of the surface finer ridges 

 connect the angles of the large triangle with those of a smaller one 

 within it. 



Column made up of transversely ridged plates with a very large 

 lumen. 



Ohservations. — From the smajl number of plates preserved and the 

 regularity of their arrangement it is not surprising that Troost mis- 

 took this specimen for a crinoid. 



The surface ridges resemble those of Chirocrinus striatus from the 

 "Lower Silurian" of Russia, but it is a smaller species with relatively 

 shorter and wider plates. 



The specific name sculptus having been used by Schmidt for an 

 European species of Chirocrinus, a new designation for the American 

 species becomes necessary. 



Formation and locality. — Although Troost's locality reference is 

 rather indefinite, the type-specimen was found undoubtedly in the 

 Middle Ordovicic shales associated with the marbles in the vicinity 

 of Knoxville, Tenn. 



Cat. No. 39951, U.S.N.M. 



Family CALLOCYSTIDiE Bernard. 



Genus TETRACYSTIS Sehuehert. 

 Tetracystis Schuchert, Smithsonian Misc. Coll., XLVII, 1904, Pt. 2, p. 217. 



TETRACYSTIS FENESTRATUS (Troost) Schuchert. 



Echinocrinites fenestratus Troost, Amer. Journ. Sci., (2), VIII, 1849, p. 419 



(nomen nudum). 

 Echino-encrinites fenestratus Troost, Proc. Amer. Ass. Adv. Sci., II (read 1849), 



1850, p. 60 (nomen nudum); MSS., 1850. — Shumard, Trans. Acad. Sci. St. 



Louis, II, 1866, p. 368 (catalogue name). — Miller, North Amer. Geol. and 



Pal., 1889, p. 241 (catalogue name). 

 Tetracystis fenestratus Schuchert, Smithsonian Misc. Coll., XLVII, 1904, p. 219, 



text fig. 26, pi. xxxiv, figs. 6-8. 



The following is quoted from Troost's original description: 



Echino-encrinites fenestratus, mihi. 



This crinoid, the summit of which is closed, and which does not possess arms, 

 approached to the genus Echino-encrinites of Herman von Meyer — Cystides of von Buch, 

 but it differs nevertheless in very important particulars from Echino-encrinites. The 

 arrangement and number of plates of which it is composed are perhaps identical with 

 those of Echino-encrinites. I say perhaps, because the five plates which form the 

 summit, as will be seen, can not be distinguished in our fossil. The other characters 

 by which it differs from the Echino-encrinites may entitle it to form a new genus. 



It has the form of a small acorn; four furrows [ambulacra a ] running longitudinally 

 from the summit to the base, divide the surface into four equal parts; on three of them 



°Additions to this description, inclosed in brackets, are by Professor Schuchert. — 

 E. W. 



