THYSANOCRINID^. 207 



Horizon and Locality. — Niagara group ; near Clifton, Wayne Co., Tenn. 



Type in the Illinois State collection, Springfield. 



BemarJcs. — We refer the above species to this genus with considerable 

 doubt, although it has close affinities with it in the structure of the dorsal 

 cup; but it differs from the typical form in having three rather large, 

 projecting infrabasals — that having apparently five — and the plates are 

 completely covered by the stem. Whether it has the same sort of ventral 

 disk cannot be ascertained from the specimen, nor do we know anything 

 about the structure of the anal side. Worthen referred the species to the 

 monocyclic genus Centrocrinus^ and apparently took the infrabasals for a 

 projecting rim of the basals. 



LAMPTEROCRINUS Eoemeb. 



I860. P. Roemer; Silur. I^auna. West. Tenn., p. 37. 



1863. Hall ; Trans. Albany Institute, Vol. IV., p. 203. 



1866. Shum. ; Trans. Acad. Sci. St. Louis (Cat. Palaeoz. Eoss., p. 378). 



1868. Hall; 20th Rep. N. York State Cab. Nat. Hist., p. 328. 



1879. ZiTTEL ; Handb. der Palseontologie, Vol. I., p. 375. 



1881. W. and Sp. ; Revision Palseocr., Part IL, p. 199 (Proceed. Acad. Nat. Sci., Phila. 1881, p. 373). 



1882. De Loriol; Paleont. Fran9aise, Tome XI. (Criuoides), p. 59. 



1885. W. and Sp. ; Revision Palseocr., Part III., p. 101 (Proceed. Acad. Nat. Sci. Phila., p. 323). 

 1889. S. A. Miller ; N. Amer. Geol. and Paleont., p. 257. 



Syn. Balanocrinus — 'Ils.oo&T, 1850 (not Agassiz, 1846), Cat. Poss. Tenn., p. 60. 



Calyx unsym metrical, elongate-obpyramidal, the rays formed into tubular 

 appendages bearing the arms. Ventral disk greatly inflated posteriorly, and 

 extended into a large tube, pushing the centre of radiation to the anterior 

 side of the calyx. 



Infrabasals anchylosed, forming a large spreading cup. Basals fiYQ, very 

 large, four of them equal, angular above; the posterior one considerably 

 higher, and truncated at the upper face. Eadials very large. Costals two, 

 the first hexagonal, the second supporting at one side a lateral arm, at the 

 other the distichals. The higher orders of radials, from the distichals up, 

 are curved like arm plates, and with the covering pieces form a rigid tube, 

 from which small arms are given off alternately at intervals. In the typical 

 species the distichals consist of three short pieces, the upper one axillary, 

 supporting at one side the second arm, at the other the palmars, of which 

 only the first plate has been observed. 



Interbrachials large, passing uninterruptedly from the dorsal cup into 

 the tegmen ; there is one plate in the first row, followed by two in the 



