246 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
plates in the third, fourth, and fifth rows, and two small plates above. Inter- 
distichal areas composed of a rather large plate, succeeded by four or five 
smaller ones. Ventral disk almost flat, with deep interradial depressions. 
Some of the plates are larger and more convex, but none of them are refer- 
able to orals. Anus subcentral, on top of a small protuberance. Column 
unknown. 
FDorizon aud Locality. — Lower Burlington limestone ; Burlington, Iowa. 
Type in the Museum of Comparative Zoblogy, Cambridge. 
Gilbertsocrinus tenuiradiatus (M. and W.). 
Plate XVII. Fig. 3. 
1869. Goniasteroidocrinus tenuiradiatus — MEEK and WortuEN; Proceed. Acad. Nat. Sci. Phila., p. 75. 
1873. Goniasteroidocrinus tenuiradiatus — MEEK and WortHEN; Geol .Rep. Illinois, Vol. V., p. 389, Plate 
1, Fig. 1. 
1881. Ollacrinus tenuiradiatus — W. and Sr.; Revision Paleocr., Part IL., p. 219. 
1889. Goniasteroidocrinus tenuiradiatus —S. A. MrtteR; North Amer. Geol. and Paleont., p. 250. 
The two specimens before us are considerably crushed, and their general 
form and the arrangement of the plates cannot be accurately determined. 
It is a larger species than the two preceding ones, with which it is found 
associated, and which it resembles in the delicacy of the plates; but in other 
respects it is more like G. typus, of a higher horizon. The surface of the 
plates is marked by a series of elevations, radiating from the middle of the 
plates to adjoming ones, which, however, are not ornamented ridges, but are 
produced by a folding of the plates. The basal concavity is quite shallow, 
and composed almost exclusively of the infrabasals. 
Basals large, curving upwards and inwards, their upper lateral faces 
longer than the corresponding lower ones; they are extended into a sharp, 
slender spine rising from the centre of the plates, unlike the case of G. typus, 
in which the spines cover the whole surface of the plate. Radials very 
large, and mounted with similar spines as the basals. Arms given off from 
the second distichals; their structure unknown. Calycine appendages very 
long, and tapering but slightly; their joints are strictly cylindrical and 
devoid of ornamentation ; they are arranged interradially in pairs, and those 
of each pair are connected laterally by zigzag sutures to the fourth or fifth 
joint, when they become free and diverge in opposite directions. The 
number of arms and the number and arrangement of interradial and inter- 
distichal plates cannot be ascertained in the specimens. 
