242 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
the other plates. Anal opening almost central. Column round, filling 
nearly the whole width of the basal concavity ; axial canal small and pent- 
angular. 
Horizon and Locality. — Highest part of the Upper Burlington limestone, 
Burlington and Pleasant Grove, Iowa. Rare. 
Type in the Museum of Comparative Zoblogy, Cambridge. 
Remarks. — In this and the two preceding species, which were the last sur- 
vivors of the genus, the individual tubes are constructed of three rows 
of plates instead of a single one as in all others. This species, however, 
differs essentially from all others in the form of the calyx. While in G. 
tuberosus and similar forms the basals form the sides of the lower concavity, 
they are placed in G. obovatus at the sides of the dorsal cup, which is 
decidedly convex in the latter, but flat or even concave in the former. 
Gilbertsocrinus typus (Hatt). 
Plate XIV. Figs. 1, 2, 3, and Plate XVII. Figs. 7a, 6. 
1859. TZrematocrinus typus — Hatt; Suppl. Geol. Rep. Iowa, p. 73. 
1872. Gilbertsocrinus (Lrematocrinus) typus— Haut; Bull. Museum Nat. Hist., Plate 6, Fig. 13. 
1873. Goniasteroidocrinus typus —Mexrxk and WortuEN; Geol. Rep. Illinois, Vol. V., p. 390. 
1881. Ollacrinus typus —W. and Sp.; Revision Palwocr., Pt. II., p. 219. 
1889. Goniasteroidocrinus typus—S. A. Mitten; North Amer. Geol. and Paleont., p. 250. 
Syn. Zrematocrinus papillatus Hatt; Suppl. Geol. Rep. Iowa, Vol. I, p. 76. 
Calyx broadly concave at the base, somewhat inflated at the middle, 
contracted near the top, spreading above into a projecting rim around the 
upper margin. Ventral disk low-hemispherical or slightly convex. Basals, 
radials, and interradials produced into sharp central spines or elongate 
nodes; all other plates convex and slightly tumid. 
Infrabasals comparatively large, forming a pentagon, of which the greater 
part is exposed beyond the column. Basals very large, curving so that the 
lower halves of the plates rest within the columnar concavity, the upper 
forming a part of the lateral walls of the dorsal cup; their spines directed 
downward, while those of the other plates are directed outward. Radials 
much larger than the costals; the interradials one half smaller, but larger 
than the interbrachials. First distichal smaller than the second, the latter 
higher and axillary, supporting two arms, which branch from the third 
5 y> I 5 ? 
palmar, and again on one side from the third post-palmar, making a cluster 
of arms to each opening. Arms pendent, long and delicate, uniserial to the 
last bifureation, when the plates become cuneate and interlock. Pinnules 
