THYSANOCRINID^. 199 



stout, widely separated. The first pinnule, which is fixed^ more erect, and 

 stronger than the others, is given off from the outer side of the second dis- 

 tichal, the second from the inner side of the fourth plate; all succeedino* 

 plates except the axillaries being pinnule-bearing. Interbrachial spaces 

 deeply depressed ; the first plate large, followed by two smaller ones, and 

 these by three in the third row, and others above. Anal side wider, some- 

 what angular along the median line ; the first anal plate resting upon the 

 truncate basal. Interaxillaries three, in two ranges ; each one marked by 

 a small, central tubercle. Construction of disk and form of anus unknown. 

 Column round, slightly tapering ; the nodal joints at their outer edges 

 faintly crenulated ; axial canal large, pentalobate. 



Horizon and Locality, — Trenton group ; Cape Girardeau, Mo., and 

 Alexander Co., 111. 



Ti/pes in the collection of S. A. Miller, Cincinnati. 



Ptychocrinus parvus (Hall). 

 Plate XVIII, Figs, la, h and 2. 



1873. Glyptocrinus parvus — Hall; Descr. New. Crin., etc., Plate 1, Kg. 17 (witliout description); also 



24it}i Rep. N. Y. State Cab. Nat. Hist., p. 207, Plate V., Fig. 17. 

 1873. Glyptocrinus 'parvus — Meek; Palseont., Ohio, Yol. I., p. 36, Plate 3, Pigs, 4rtr, I. 

 1879. Glyptocrinus annularis — Millee and Dyeh; Journ. Cincin. Soc. Nat. Hist., Plate 1, Pig. 10. 



1QQ-, J ffPiocrinus parvus ) _w. .^^ Sp. ; Revision Pala^ocr., Part 11, pp. 188, 189; and Amer. 

 1881. <; Glyptocrinus angulans \ , j^^^^_ g^._^ ^ggg^ ^^j_ ^^^ ^ ^^^ 255-268. 



1881. Reteocrinus gracilis — Wetherby; Cincin. Journ. Nat. Sci., Yol. lY., Plate 3, Pig. 2. 



( Glyptocrinus parvus \ — S. A. Miller, Journ. Cincin. Soc. Nat. Hist., Yol. YI., pp. 234 and 

 I Gaurocrinus angularis ) 339 ; and 1889, North Amer. Gaol, and Palseont., pp. 347 and 348. 



1885. i ^ty^hocrinus parvus \ _ -^ ^^^^ g^^ . j^^^.^-^^ Pal^ocr,, Part III., p. 100. 



( Ptychocrinus angularis ) 



Of small size. Calyx obconical, with slightly convex sides; the radial 

 plates marked with prominent rounded ridges, which extend to nearly the 

 full width of the plates -, interbrachial spaces flat, plates very slightly con- 

 vex and without ornamentation. 



Infrabasals minute, only the outer angles of the plates visible beyond 

 the column. Basals large, higher than wide ; their surfaces strongly convex. 

 Interbasal sutures deeply depressed, and the depression continued to the 

 radials, of which the lower ends bend inward. Eadials somewhat larger than 

 the first costals. The second costals of similar form to the radials, only 

 reversed, being angular above instead of below. Distichals 2 X 10, about as 

 wide as long, the upper one axillary. Arms four to the ray, free from 



