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



but it seems to me that the articulation of the valves by distinct 

 teeth and the presence of a distinct hinge-area are quite sufficient 

 characters to separate the two generieally. Whether Productella can 

 be kept apart from Strophalosia, King, is another matter, the chief 

 characters by which the two are separated being merely questions of 

 degree. In external appearance, however, the shells referred to 

 Productella resemble Producta much more nearly than do those re- 

 ferred to Strophalosia. 



Hall has described many species of Productella from the Devonian 

 rocks of the State of New York, chiefly from the Hamilton and 

 Chemung groups, but also from the Corniferous Limestone. I have 

 only met with a single species of the ^enus in the Devonian rocks 

 of Western Ontario ; but this, though exceedingly abundant in the 

 Corniferous Limestone of various localities, seems to be distinct from 

 any recorded by Hall, and I shall therefore describe it as new, 

 PRODtJCTELLA Eriensis, Nicholson. PL VI. Fig. 10. 



Shell minute, thick, semi-oval, or nearly semi-circular, the length 

 about one-fourth less than the width as a general rule. Hinge-line 

 as wide or wider than the greatest width of the shell ; the cardinal 

 angles rounded or more commonly auriculate. 



Ventral valve exceedingly gibbous and ventricose, strongly and 

 regularly arched from the beak to the front margin, but depressed 

 towards the cardinal angles. Umbo obtuse, prominent, strongly 

 incurved. Area very narrow and difficult to make out. 



Dorsal valve depressed convex, not gibbous, depressed towards 

 the cardinal angles. When partially decorticated, it shows very dis- 

 tinctly from six to eight concentric imbricating lines of growth. 

 In this condition it also exhibits a more or less defined median 

 longitudinal ridge, which extends from a small elongated pit just in 

 front of the umbo to the front margin — two generally stronger ridges 

 diverging from the umbo on either side of the central ridge. The 

 beak is scarcely prominent, whilst there is an extremely narrow 

 linear area and a small cardinal process. 



The cast of the ventral valve exhibits a long-itudinal slit extending 

 from the beak about one-fourth or one-third of the shell, and indi- 

 cating that the cavity of the beak was divided by a low mesial 

 partition ("rostral septum"). In front of this slit there is often a 

 horseshoe-shaped elevation representing the cast of the pit where 

 the divaricator muscles were attached; but this is not always con- 

 spicuous. On one or both sides of the mesial slit there is also 

 generally a slighter and shallower grove bounding the umbo laterally, 

 but the general surface of the cast is quite smooth and not pitted. 



The interior of the dorsal valve exhibits radiating lines of minute 

 pits, which cover its whole surface, or are most abundant in the 

 central portion of the valve, and diminish us the margin is ap- 

 proached. Besides these, on either side of the middle line are two 

 pairs of deep slightly curved sulci, which extend from beneath the 

 beak to near the margin. Those of the innermost pair are most 

 constant, and are placed close to the central line of the valve. Those 

 of the outer pair are more variable, and there are often two or three 



