THE CARBONIFEROUS OF NORTHUMBERLAND. T47 
Lepidodiscus was to a certain extent collapsible, and that the upper 
ray-plates could be more or less drawn in when the animal assumed 
its retracted or uninflated state. 
The interbrachial area enclosed between the single dextral ray 
and the sinistral one which stands opposed to it is subtriangular in 
contour and larger than any of the other areas; it contains also an 
orifice, situated in the angle formed by the curve of the sinistral 
ray, which was originally closed by narrow wedge-shaped plates, 
and was in all probability the periproctium, and the homologue of 
the anal tube of Crinoids. 
The imperfect preservation of the part of the disk just mentioned 
prevents, unfortunately, the extremity of the odd dextral ray being 
followed to its final termination. This ray, after extending for 
some distance along the area within the curve of the sinistral ray, 
bends inward towards the periproctial aperture, and is lost in the 
confusion which occurs amongst the plates in that vicinity. 
The surface of the plates is finely granular, and when magnified 
is seen to be densely covered with accurately rounded spherules; no 
order is traceable in their arrangement on the plates of the inter- 
radia ; but on those of the rays the granules show a tendency to run 
into one another, and usually assume a linear arrangement across 
the plates. 
Absolutely nothing can be said respecting the under surface of the 
present fossil, and hardly any light, beyond the record Forbes has given 
of the fragmentary structures preserved in Agelacrinites Buchianus*, 
has yet been thrown upon the structure of this part of the Agela- 
crinitide by any specimens hitherto described. In commenting upon 
an example of Lepidodiscus cincinnatiensis, Romer, found at Rich- 
mond, Indiana, which seemed “to have grown on one of the valves 
of an Ambonychia, and from which the shell had separated in such 
a manner as to take with it the underside of the Agelacrinites, and 
leave its upperside in the matrix so situated as to expose its inner 
surface,’ Mr. Meek? states that ‘“‘the inner side of each arm or 
ray is here seen to be composed of a single series of quadrangular 
pieces that are not imbricating, while the disc-plates near the outer 
margin show, on their inner surfaces, little parallel ridges, directed 
inward, and apparently fitting into corresponding furrows in the 
lapping edges of the contiguous pieces.” Of the plates mentioned 
above as forming the floor of the radii, there are indications in the 
present specimen, at the broken extremity, of more than one of the 
rays; but respecting their individual form in this species, or of the 
other structures observed by Mr. Meek, it is impossible to speak. 
The dimensions of the specimen are as follows :—the greater dia- 
meter measures 0:98 of an inch, the lesser 0-8; breadth of a ray near 
the inner extremity about 0-07. 
Remarks.—The specimen has been crushed and somewhat distorted 
prior to or during the process of fossilization, and its margin has also 
suffered considerable damage when the matrix was first roughly 
* Mem. Geol. Survey, vol. ii. pt. 2, p. 522. 
+ Geol. Sury. Ohio, vol. i. pt. 2 (Paleont.), p. 55. 
