THYS ANOCEINID^ . 197 



six interbrachials shown, arranged : 1, 2, S; 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. 



Horizon and Locality. — Niagara group (?) ) near Louisville, Ky. 



Bemarhs. — 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. 



PTYCHOCmNUS W. and Sp. (Emend.). 



1885. W. and Sp. ; Eevision Palseocr., Part III., p. 99 ; also Proceed. Acad. Nat. Sci. Pliila., p. 821. 



Sjn. Gl^ptocrinus (ui^d.Ti)—llKL-L, 1872, 24th Pep. N. York State Cab. Nat. Hist., p. 207; also 



Miller and Dyer, 1878, Journ. Cincin. Soc. Nat. Hist., Plate 1, Pig. 10. 

 Syn. Gaurocrinus (in part) — S. A. Miller; 1883, Journ. Cincin. Soc. Nat. Hist., p. 228; and 1889 



N. Amer. Geol. and Paleeont., p. 276. 



Specimens small ; in form and mode of ornamentation resembling Glypto- 

 emus. 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 ^Ye, small, but generally visible beyond the column. Basals 

 ^Ye, 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 Avith 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 : Ptychoerinus splendens (S. A. Miller). 



Bemarhs. — Ptycliocrinus differs from Tliysanocrinus in having delicate 

 uniserial arms^ from Beteocrinus in the definite arrangement of its inter- 



