Prof. H. A. Nicholson — New Devonian Fossils. 119 



radiating grooves on either side in place of one. Immediately 

 beneath the beak, lastly, are placed two elongated grooves, one on 

 each side, which only diverge slightly from the direction of the 

 hinge-line, and extend only a short way into the shell. These are 

 apparently dental sockets. 



The surface of the ventral valve is rarely preserved, but appears 

 to have been quite smooth. The surface of the dorsal valve exhibits 

 faint concentric strise. No radiating striae can be made out, nor 

 are there any traces of spines either on the hinge-line or upon the 

 surface of cither valve. 



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 in a large number of 

 specimens ; but a few individuals are veiy slightly larger, and many 

 have the proportion of the length to the width slightly less, owing to 

 the greater extension of the cardinal angles. 



Amongst the numerous species of Productella described by Prof. 

 Hall from the Devonian rocks of the State of New York, there are 

 only P. sub-aculeata and P. Fullia which have the dorsal valve con- 

 vex, all the others being concavo-convex. From these, however, as 

 indeed from all the rest, P. Eriensis is distinguished by the total 

 absence of spines and by the internal 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 unfortunately insufficient ; since, though I have ex- 

 amined some hundreds of specimens, I have not succeeded in finding 

 a single example in which the characters of the hinge-line and areas 

 are satisfactorily shown. Still, the ventral valve, in its great gib- 

 bosity, its extended hinge-line, and its produced and depressed ears, 

 is singularly Productoid ; and the presence of distinct areas on each 

 valve, together with 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 Productella. The muscular im- 

 pressions in the ventral valve unluckily cannot be made out, and 

 no help consequently can be derived from this source ; whilst the 

 interior of the dorsal valve is certainly unlike that of the typical 

 ProductellcB, and in some respects approaches Leptoena. 



Productella Eriensis presents a considerable superficial resemblance 

 to Spirifera lorii, Fleming; but the latter has a hinge-line shorter 

 than the greatest width of the shell, rounded cardinal angles, both 

 valves with mesial furrows, and a sufficiently conspicuous area. 

 Our species is also very like Ambocoelia umhonata, Conrad (= Orthis 

 umbonata, Conrad, and 0. nucleus, Hall), which is very closely 

 allied to Spirifera lorii. The latter, however, is distinguished from 

 P. Eriensis by its very elevated umbo, the existence of a well-marked 

 mesial sinus in the ventral valve, and the presence of a comparatively 

 large and high area, which extends conspicuously to the cardinal 

 extremities. 



