THE CARBONIFEROUS OF NORTHUMBERLAND. 745 
Subsequently Prof. Lebour kindly entrusted his specimen to the 
writer for examination, when, after carefully cleaning away the 
obstructing film of matrix which covered a great portion of the disk, 
it was at once evident that the fossil was distinct from any hitherto 
recorded. 
I have very much pleasure in associating the name of my friend 
with this species, of which the following description will furnish 
the characters :— 
Leprpopiscus, Meek and Worthen, 1868. 
Leprpopiscus Lezourt, sp. noy. Plate XX XVII. 
Agelacrinites (Lepidodiscus) squamosus, Lebour, Ann. de la Soc. 
Géol. de Belg. t. ii. p. 21 (non Meek and Worthen). 
Body depressed, discoid or subconoid in form, marginal contour 
slightly oval; covered with imbricating plates. The rays, which 
are Six in number, are elevated in relief above the plane of the disk, 
and are long, narrow, and strongly curved in semispiral (five sinistral 
and one dextral), as they radiate from the centre to the periphery, 
parallel with the margin of which they are prolonged for some 
distance. The apical portion of the disk, which is formed by the 
common union of the radii, consists of seven or eight irregular 
plates, compactly fitting to one another, which form an uninterrupted 
and continuous surface with the plates which belong to the radial 
series. The brachial plates may consist either of broad, short*, 
band-like plates, which span across the ray, or (more frequently ?) 
of alternating pairs of wedge-shaped pieces, the elements of the 
pairs being reciprocal and presenting every degree of relative pro- 
portion. On account of this irregular development there is an 
absence of uniformity in the arrangement of the plates, especially 
in the middle portion of the ray; and this is further augmented by 
a tendency to division manifest in some of the plates. A careful 
study of the specimen leads to the conclusion that the wedge-shaped 
plates are consequent on a certain retardation of development, and 
that the result is produced somewhat after the following manner :— 
A ray-plate, by reason of retardment of development, has its distal 
margin sloped away, thus producing a wedge-formed piece, which of 
necessity requires a corresponding modification of the succeeding 
plate, in order to maintain the equilibrium of the series. Two 
alternating wedges are the result. The stages of diminution or 
retardment of development are present in every degree, the size of 
the companion plate varying proportionally and reciprocally. It 
frequently happens that two neighbouring plates have the proximal 
_ margin of the inner and the distal margin of the outer plate, on the 
* It may be well to explain that the terms of length and breadth used 
throughout this paper are applied to the plates in respect to their proportions 
when in natural position on the organism, and do not necessarily correspond 
with those which would be employed when familiarly describing the same 
object in an ¢solated state. Thus, in the present case, length is measured 
between the proximal and distal margins, and breadth is the extent across 
the ray. 
