Agelacrinidae and Lepadocystinae 
419 
The presence of floor plates is readily verified among Ordo- 
vician species referred to Agelacrinus and Lepidodiscus , provided 
that the overlying cover plates are carefully removed. They are 
seen also frequently among the displaced plates of specimens 
which had more or less disintegrated before being covered by the 
sea sediment. 
In the Geological Museum of Ohio State University, there is a 
specimen of Agelacrinus cincinnatiensis , showing a series of three 
floor plates in a single row (plate I, Fig. 6C). In this case it is 
evident that the median part of each plate, as seen from above, was 
depressed into a wide groove, while a narrow groove extended 
lengthwise along the border, on each side of the wide median 
groove. The wide median groove evidently formed part of the 
ambulacral furrow, while the narrow lateral grooves had some 
connection with the fulcra of the lateral covering plates, by means 
of which the latter were opened and closed over the ambulacral 
furrow. 
In the type of Agelacrinus faheri, forming No. 8821 in the Faber 
Collection in Walker Museum, at Chicago University, possib]}^ 
identical with the species from which Meek described the presence 
of floor plates, a few floor plates were identified (plate I, Fig. 3C), 
and plate II, Fig. 4), among the mixture of plates there presented. 
Three of these floor plates occurred in a single row. Little could 
be learned from them beyond the fact that these plates are widely 
grooved along the top, as though the plates were almost evenly 
concave. They evidently overlapped a little in a proximal direc- 
tion, as seen from above. The narrow lateral grooves, one on each 
side of the broad median groove, could not be identified. They 
may have been present formerly, but the floor plates are badly 
weathered. 
In the type of Agelacrinus holhrooki, forming No. 1004, in the 
James Collection, in Walker Museum, at Chicago University, a 
series of five floor plates belonging to the left ray (No. 2) are 
preserved (plate I, fig IE). Of these, the three floor plates which 
belong to that part of the ray which is parallel to the peripheral 
ring, show a comparatively narrow median ambulacral groove, and 
unusually strong lateral grooves which have some connection with 
the articulation of the lateral covering plates. In the case of two 
other plates belonging to the same series, but located nearer the 
proximal end of the ray, the median, ambulacral groove was much 
