28o The American Geologist. Xovember, i904. 
Figure 53 has apparently five basals and a pentagonal 
stem base. Hie jjlates are ornamented by small nodes and 
ridgies bordering the sutures. From the Niagara of Ste. Gene- 
vieve county. 
Crixoid plates. 
Plate XVr. Figs. 49,51. 
These plates perhaps belong to some species of Lamptero- 
crinus, Clinto. . oolite. Pike Co., '\lo. 
Cystoid Plates. 
Plate XVI. Figs. 47, 50, 52. 
These arc found associated with the crinoid plates above. 
A single plate of Caryocrinus oniatiis was found at the St. 
]\Iary's localitv, but the writer failed to find Edriocrinus in 
the Delthvris beds at Red Rock Landing. 
Skenidium? nodocostatum, n. sp. 
Plate XVI. Figs. 60, 61, 62, 63. 
This little shell has some external resemblance to Orthis. 
However, the few. strong plications, rather high cardinal 
area and other features separate our species from that form 
and, as it bears a strong resemblance to Skenidium we have 
ventured to place it under that genus, in the absence of struct- 
ural material. 
The cardinal area is less than the width of the shell, not 
high and with an uncovered deltidium whose sides are almost 
parallel. The brachial valve is somewhat convex with a broad 
illy defined sinus occupied by twO' plications smaller than the 
ones bounding the area. Either side of the sinus is covered by 
three strong plications with three other smaller implanted 
ones, not reaching the beak. 
The pedicel valve is slightly more convex than the brach- 
ial without fold, but with a strong central plication. Either 
side of this central costa are three strong ribs or plications 
with an equal number of smaller implanted ones as on the 
brachial valve. 
The beak of the brachial valve protrudes lieyond the car- 
dinal area of the pedicel valve, displaying a narrow brachial 
area. The beak of the jiedicel valve is alnux^t retrorse. 
