THYSANOCRINIDZ. 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 succeeding 
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., Il. 
Types in the collection of S. A. Miller, Cincinnati. 
Ptychocrinus parvus (H411). 
Plate XVII, Figs. 1a, 6 and 2. 
1872. Glyptocrinus parcus — Hau; Descr. New. Crin., efe., Plate 1, Fig. 17 (without description) ; also 
24th Rep. N. Y. State Cab. Nat. Hist., p. 207, Plate V., Fig. 17. 
1873. Glyptocrinus purcus — MEEK; Paleont., Ohio, Vol. I., p. 36, Plate 2, Figs. 4a, 4. 
1879. Glyptocrinus angularis— Mit1ex and Dyer; Journ. Cincin. Soc. Nat. Hist., Plate 1, Fig. 10. 
Glyptocrinus ee ) —W. and Sp.; Revision Paleocr., Part II., pp. 188, 189; and Amer. 
er Giyuincrams® creat Journ. Sci., 1883, Vol. XXV., pp. 255-268. 
Reteocrinus gracilis 
1881. Reteocrinus gracilis — WETHERBY ; Cincin. Journ. Nat. Sci., Vol. IV., Plate 2, Fig. 2. 
{ Glyptocrinus parvus ay A. Mitter, Journ. Cinein. Soc. Nat. Hist., Vol. VL, pp. 224 and 
| Gaurocrinus angularis 229; and 1889, North Amer. Geol. and Paleont., pp. 247 and 248. 
1sss. § Plychocrinus parcus | __w_ and Sp.; Revision Paleoer., Part IIL, p. 100. 
| Ptychocrinus angularis j 
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. Radials 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 
