sT 
~I 
and the anterior extremity of the mesial septum. The cardinal process, seen from the inner 
side, is bilobed, and from the exterior side each of these divisions is usually bilobed. 
“These shells differ from Strophalosia in the extremely narrow linear cardinal area, 
greater extension of the hinge-line, more extreme arcuation or ventricosity of the ventral valve 
in many or most of the species, and especially in the direction and termination of the reniform 
vascular impressions, which resemble those of Awlosteges, and of some species of Productus. It 
differs from Productus in tne constant presence of an area, hinge-teeth, and sockets.” (Hall, 
Pal. New York, Vol. IV., p. 153). 
Productella is considered by Hall as a mere sub-genus of Productu, 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 Productella generically from Producta. Whether 
Productella can be kept apart from Strophalosia of 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 
referred to Strophalosia. 
Professor 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 form of the genus in the Devonian 
formation of Western Ontario, and this. though exceedingly abundant in the Corniferous 
Limestone in several localities, is certainly distinct from any of those recorded by Hall. I 
shall, therefore, describe it as new, under the name of Productella Eriensis. 
93. PRopucTELLA Ertensis (Nicholson). 
Shell minute, thick, semi-oval or nearly semicircular, the length about one-fourth less 
than the width as a general rule. Hinge-line as wide as, or wider than, the greatest width of 
the shell; the cardinal angles rounded, or, more commonly. distinctly 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. The cast of the ventral 
valve exhibits a longitudinal slit extending from the beak about one-fourth or one-third of the 
length of the shell, and indicating that the cavity of the beak was divided by a low mesial 
partition (“rostral septum’’). In front of this slit there is often a horse-shoe-shaped elevation 
representing the cast of the pit to which the divaricator muscles were attached, but this can- 
not always be made out. On one or both sides of the mesial slit there is also gencrally a 
slighter and shallower groove bounding the umbo laterally ; but the general surface of the cast 
ig quite smooth and not pitted. 
Dorsal valve depressed-convex, not gibbous, depressed towards the cardinal angles. When 
partially decorticated, the dorsal valve shows very distinctly 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, but constant elongated pit, placed just in front 
of the umbo, to the front margin—two generally stronger ridges diverging outwards, one on 
each side of the central line, from the umbo towards the margin. The beak of the dorsal 
valve is scarcely prominent, whilst there is an extremely narrow linear area, and a small car- 
dinal process. 
The interior of the dorsal valve exhibits radiating lines of minute elongated pits, which 
cover its whole surface, or are most abundant in the central portion of the valve, and diminish 
as the margin is approached. 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 quite close to the central line of the 
valve. Those of the outer pair are more variable, and there are often two or three radiating 
grooves on either side in place of only 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 distance into the shell. These are apparently dental sockets. 
The surface of the vental valve is rarely preserved, but appears to be quite smooth ; the 
surface of the dorsal valve exhibits faint concentric striz. No radiating striz can be made 
out; nor are there any traces of spines either on the hinge-margin of the ventral valve or — 
upon the surface of either valve. 
