78 



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, and 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. 

 subaculeata and P. Tullia, which have the 

 , dorsal valve convex, all the others being 



a, Exterior of the dorsal valve of Productella Eriensis, [Nichol- ' 



son] partially exfoliated, enlarged ; 6, cast of the ventral valve of a COncavO-COnvex. r rom these, however, 



rather larger individual of the same, enlarged; c, interior of the i nf j ppf ] f rnrn !! *}, * 



dorsal valve of the same, enlarged ; d, cast of the ventral valve of an 3S . *? e . l est > 



individual with unusually extended ears, enlarged. All from the Cor- Eri&nsis is readily distinguished by the 



niferous Formation. L i i j 11 1 , 



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 of 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 Producta, and would seem to warrant its reference to Produc- 

 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 Leptwna. 



There remain two well known Devonian Brachiopods to which at first sight the present 

 form bears afar from slight resemblance, viz., the Spin/era Urii of Fleming, and the Spin/era 

 (Ambocoelia) 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- 

 sal 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. 



Ambocazlia umbonata (Conrad), \0rthis vmhona, Conrad, and Orthis nucleus, Hall,] is 

 also a small semi-circular Brachiopod, which is very nearly related to Spirifera Urii. It pre- 

 sents a superficial resemblance to Productella 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 striae. 



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 

 iu front by a deltidium. Dorsal valve convex and often very ventricose, with or without a 



