678 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
torted, much smaller specimen, with smooth plates. In the type of P. prat- 
tenanus, which preserved its natural form, the rim around the base projects 
more than in the type of P. Sare as figured by Hall, but the base is not 
correctly represented in that figure. P. monroensis is a very young speci- 
men in which the arms are as yet uniserial, zigzag, and the plates wedge- 
form, with nothing to indicate that it differed from the preceding forms. 
Platycrinus Huntsville Troost MS. 
Plate LX XIII, Figs. 6, 7a, 6, 8, 9, 10, 11, 12. 
1849. Troost; Proceed. Amer. Ass. Adv. Sci. of 1849, p. 61 (without description). 
Syn. Platyerinus penicillus M. and W., 1860; Proceed. Acad. Nat. Sci. Phila., p. 880; also Geol. 
Rep. Illinois, Vol. IL., p. 266, Plate 19, Figs. 6a, 4, c. 
Syn. Platyerinus plenus M. and W., 1860; Proceed. Acad. Nat. Sci. Phila., p. 8380; also Geol. Rep. 
Illinois, Vol. IT., p. 267, Plate 20, Fig. 3. 
Syn. Platycrinus alabamensis 8. A. Minter, 1891; Adv. Sheets 17th Rep. Geol. Surv. Indiana, p. 50, 
Plate 9, Mie. 5. 
An extremely variable species of the type of P. Sarw, varying consid- 
erably in the form and ornamentation of the calyx plates and in the number 
0 SSS SS SS 
of arms; but readily recognized by the peculiar and unique form of the | 
| brachials, and the presence of a large pinnule upon the first distichals and : | 
i | first palmars. Dorsal cup generally a little wider than high, cup or bowl- | 
Nt shaped ; the sides in most of the specimens nearly straight, curved longi- 
AHL | tudinally, but sometimes distinctly convex and constricted at the arm 
| ie regions; base of the cup rather broadly truncated. 
eee 
| Basals forming a short saucer-shaped cup with a flattened or slightly 
ae concave lower face, which exceeds the width of the stem at the upper end; 
| the interbasal sutures visible by moistening the specimens, their lines highly 
| elevated above the surface, and formed into ridges which at the lower edges 
of the cup terminate in small tubercles. Radials subquadrangular, about as 
wide as long in mature specimens, proportionally a little shorter in the 
younger ones; the sides very slightly expanding; the superior lateral angles 
distinctly truncated. Facets directed upward; small, occupying only one third 
the width of the plates, and extending but a short distance downward. Cos- 
tals trigonal, much wider than long, occupying the full width of the facets ; 
the superior faces concave, and indented at the median portions for the 
reception of small processes passing out from the lower edges of the dis- 
tichals, and forming waving sutures, which resemble those of the Ichthyo- 
crinide, Similar suture lines occur between the distichals, palmars, and | 
