750 W. P. SLADEN ON LEPIDODISCUS LEBOURI FROM 
to be noted that Z. Lebowrt is distinguished from L. squamosus by 
haying six rays, which are, moreover, proportionally narrower than in 
the American fossil, and very slightly tapering. The two remaining 
species of Lepidodiscus (L. cincinnatiensis, Romer, and L. pileus, 
Hall, both from the Lower Silurian) are differentiated from our 
species still further than those which have been compared above. 
LL. Lebourt is also very distinct from each of the European Agela- 
erinitide. The Devonian species (A. rhenanus, Romer), however, 
presents a feature which is interesting when compared with the 
present Cystid ; the fossil, which is imperfectly preserved, is repre- 
sented as possessing a single series of broad plates which span the 
rays, a character hitherto looked upon with doubt, and considered 
as abnormal amongst the group, but which now, when viewed by the 
side of ZL. Lebouri, will be regarded as presenting a stage in the 
series, although an extreme type, it is true, and difficult to associate 
with our present knowledge of the forms of Agelacrinitide. 
The following list indicates the stratigraphical distribution of the 
group, as well as the generic subdivisions into which they have been 
classified :— 
AGELACRINITIDA. 
(a). A@HLACRINITES, Vanuxem. 
(Plates of the interradia not imbricating ; radii curved.) 
A. Buchianus, Forbes. Lower Silurian: Bala Limestone. 
A. Dicksoni, Billings. Lower Silurian: Trenton Limestone. 
?A. vorticellata, Hall. Lower Silurian: Cincimnati group. 
? A, | Edrioaster| Bigsbyi, Billmgs. Lower Silurian: Trenton Limestone. 
A. hamiltonensis, Vanuxem. Devonian: Hamiliton group. 
A. rhenanus, Romer. Devonian: Hifel Limestone. 
A. kaskaskiensis, Hall. Lower Carboniferous: Kaskaskia Limestone. 
((). Lerrpopiscus, Meek and Worthen. 
(Plates of the interradia imbricating ; radii curved.) 
L. cincinnatiensis, Romer. Lower Silurian: Cincinnati and Trenton 
Limestones. 
L. pileus, Hall. Lower Silurian: Cincinnati group. 
LL. squamosus, M. & W. Lower Carboniferous: Keokuk group, 
LL. Lebouri, Sladen. Lower Carboniferous: Bernician beds. 
(y). Hemicysrrrus, Hall. 
(Radii straight.) 
H. | Agelacrinites| bohemicus, Romer: Lower Silurian. 
H. | Agelacrinites| Billingsti, Chapman. Lower Silurian: Trenton Lime- 
stone. 
FZ, stellatus, Hall. Lower Silurian: Cincinnati group. 
? H, (Cystaster) granulatus, Hall. Lower Silurian: Cincinnati group. 
H. parasitica, Hall. Upper Silurian: Niagara group. 
Locality and Horizon.—Prof. Lebour has kindly given me details 
of the geological position of this Cystidean, which was found by him’ 
in an impure limestone cropping out in the river Rede, where it 
forms a low water-fall just north of the bridge above the village of 
