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The width of the hinge-line of the ventral valve is two lines, the length about a line and 
two-thirds, and the height about three quarters of a line to a line. The dimensions of the 
dorsal valve are the same, except that the height is much less. Hardly any departure from 
these measurements can be observed, even amongst a large number of specimens, but a few 
individuals are very slightly larger, apd a good many have the proportion of the length to the 
breadth slightly less, owing to the greater extension of the cardinal angles, 
Amongst the numerous species of 
Productella described by Professor Hall 
from the Devonian Rocks of the State of 
New York, there are only two, viz., P. 
Fig. 26. subaculeata and P. Tullia, which have the 
a, Exterior of the dorsal valve of Productella Eriensis, [Nichol- dorsal valve CORNER; all the others being 
son] partially exfoliated, enlarged ; b, cast of the ventral valve of a CONCaVO-CONVEX, From these, however, 
forsal valve of the same, enlarged d, cast of the ventral valve ofan 28 indeed from all the rest, Productella 
individual with unusually extended ears, enlarged. All from the Cor- Eriensis 1s readily distinguished by the 
niferous Formation. > i ) 
total absence of spines, and by the inter- 
nal characters of both valves. There may, in fact, be some doubt as to the reference of this 
form to Productella at all, and for the positive decision of this doubt our materials are unfor- 
tunately insufficient; since, though I have examined some hundreds ot specimens, I have 
not succeeded in finding one single example in which the characters of the hinge-line and 
areas are satisfactorily shown. Still the ventral valve, in its great gibbosity, in its extended 
hinge-line, and its produced and depressed ears, is singularly Productoid ; and the presence 
of distinct areas in each valve, and the fact that the valves are articulated by teeth and sockets, 
would remove the species from Producfa, and would seem to warrant its reference to P:oduc- 
tella. ‘The muscular impressions in the ventral valve, unluckily, cannot be made out, and con- 
sequently no help can be derived from this source ; whilst the interior of the dorsal valve is 
certainly unlike that of the typical Productella, and in some respects approaches Leptcna. 
There remain two well known Devonian Brachiopods to which at first sight the present 
form bears afar from slight resemblance, viz., the Spirifera Urii of Fleming, and the Spirifera 
(Ambocelia) umbonata of Conrad, and it may therefore be as well to indicate the points by 
which our species is distinguished. 
Spirifera Urii (Fleming), is a small suborbicular shell with a very convex and gibbous 
ventral valve, a prominent and incurved umbo, and a semi-circular flat or slightly convex dor- 
gal valve. The hinge-line, however, is shorter than the greatest width of the shell; the car- 
dinal angles are rounded; the dorsal valve has a shallow mesial furrow which commences 
near the beak and extends to the front; the ventral valve has a longitudinal furrow commen- 
cing at the extremity of the beak and extending to the front ; and there is a sufficiently 
conspicuous area. These characters fully distinguish Spirifera Urii from Productella Eriensis. 
Ambocelia umbonata (Conrad), [Orthis wmbona, Conrad, and Orthis nucleus, Hall,| is 
also a small semi-circular Brachiopod, which is very nearly related to Spirifera Urit. Tt pre- 
seats a superficial resemblance to Productellu Eriensis, owing to its gibbous ventral valve, and 
comparatively wide and straight hinge line. It is however, readily distinguished by its 
very elevated umbo, the existence of a mesial sinus in the ventral valve extending from the 
beak to the front of the shell, and the presence of a comparatively large and high area, which 
extends “ conspicuously to the cardinal extremities.” The surface also is marked by fine 
radiating and concentric striz. 
Locality and Formation.—Very abundant in certain beds of the Corniferous Limestone 
at Port Colborne and Hagersville. 
Genus ATRYPA (Dalman). 
‘ 
Shell impunctate and fibrous; surface usually ribbed and often furnished with imbri- 
cating lines of growth often produced into foliaccous expansions; valves articulated by teeth 
and sockets ; the ventral valve often depressed in front, with or without a mesial sinus, its 
beak incurved and perforated at the apex by a minute foramen, which is sometimes bounded 
in front by a deltidium. Dorsal valve convex and often very ventricose, with or without a 
