THYSANOCRINID.E. 197 
six interbrachials shown, arranged: 1, 2,5; but there were probably others 
above. The anal interradius apparently has two plates in the second row, 
but the middle one of the next row extends half way down into the second. 
Florizon and Locality. — Niagara group (?); near Louisville, Ky. 
Remarks. — The type specimen, which was said to be in the Knapp col- 
lection, cannot be found. The two specimens here figured, from the 
Borden Institute of New Providence, Ind., are both somewhat abnormal and 
quite fragmentary, and leave some doubt as to the generic relations of the 
species. Not only is the anal plate followed by only two plates, but the first 
regular interbrachial occasionally touches the basals. 
PTYCHOCRINUS W. and Spr. (Emend.). 
1885. W. and Sp.; Revision Palexocr., Part III., p. 99; also Proceed. Acad. Nat. Sci. Phila., p. 321. 
Syn. Glyptocrinus (in part) — Hatz, 1872, 24th Rep. N. York State Cab. Nat. Hist., p. 207; also 
Miller and Dyer, 1878, Journ. Cincin. Soc. Nat. Hist., Plate 1, Fig. 10. 
Syn. Gaurocrinus (in part) —S. A. Minter; 1883, Journ. Cincin. Soc. Nat. Hist., p. 228; and 1889 
N. Amer. Geol. and Paleont., p. 276. 
Specimens small; in form and mode of ornamentation resembling Glypto- 
crinus. The radial plates marked by a well defined ridge, which passes up 
and down the median line of the plates, giving to the interradial spaces 
a somewhat depressed appearance. 
Infrabasals five, small, but generally visible beyond the column. Basals 
’ five, large; four of them hexagonal, the posterior one heptagonal, truncate 
above. Radials and costals of nearly equal size. Costals two. Distichals 
varying in number, curved like arm plates. Arms ten to twelve, rather 
delicate, and uniserial. Pinnules strong. Interbrachials and interdistichals 
not numerous, the plates definitely arranged. Posterior side with a longi- 
tudinal row of anal plates forming a ridge. The first anal plate in a line 
with the radials, and always succeeded by a row of three plates, — a second 
anal and two interbrachials. Structure of ventral disk imperfectly known. 
Column cylindrical; axial canal large, pentalobate, the lobes directed 
radially. 
Distribution. — Restricted to the Trenton and Hudson River groups of 
America. 
Type of the genus: Ptychocrinus splendens (S. A. Miller). 
Remarks. — Ptychocrinus differs from Thysanocrinus in having delicate 
uniserial arms; from Meteocrinus in the definite arrangement of its inter- 
