1102 General Notes. 
and about three and one-half centimeters in height; inequivalve 
hinge line sometimes (in both young and old specimens) extremely 
produced into wing-like expansions; at other times the hinge line 
equalling, or much less than the greatest width of the valves below; 
again, some specimens (old and young) are longer than wide; at 
other times wider than long, even though the hinge line is not pro- 
uced. 
Dorsal valve generally regularly convex, but sometimes flattened 
on the cardinal extremity; greatest convexity at or a little above 
the middle; beak incurved slightly beyond the hinge line; mesial 
fold often not defined; at other times slightly defined; and rarely 
strongly and sharply defined in front. i 
Ventral valve gibbous at or above the middle, having twice as 
great an elevation as the opposite valve; beak generally much ex- 
tended above the hinge line, but sometimes scarcely ; sharply in- 
curved, or not incurved; sinus sometimes wanting, at other times 
shallow and scarcely defined above the middle, and producing a 
slight sinuosity (at times strongly produced) in front; in some speci- 
mens with greatly produced hinge lines, the sinus is quite well de- 
fined nearly or quite to the beak; area large and well defined, prin- 
cipally confined to the ventral valve, vertically striated; foramen 
narrow, triangular, extending quite to the open valve, the margins 
or dental lamellæ often a little projecting.. Surface marked by fine 
rounded radii; radii about equal to the space between them, “and 
both are again finely striated in the same direction by microscopic 
lines, and the whole crossed by fine striæ which give a granulat 
appearance to the uneven surface”; this feature, however, is not al- 
ways well shown even in well-preserved specimens. fees 
The “dichotomising of the radii on the mesial sinus and fold is 
by no means a constant feature. The internal structure of this 
shell varies considerably in different individuals. The dental la- 
mella, which is usually very strong, generally extends to the centre 
of the valve, and there becomes obsolete; these lamellæ gradually 
diverge downward and about the ċentre of the valve, between 
them, is a deep heart-shaped muscular impression, marked by toa 
to six more or less prominent vertical striæ; the dental lamel æ 
sometimes extend to the centre of the shell only as slight elevations 
along the margins of the muscular impressions; the muscular 1m- 
pressions vary somewhat in size, depth and general form in differ- 
ent specimens. -t ae 
_ dn some instances, the interior of the ventral valve is distinct y 
punctate; cardinal processes of dorsal valve rather large, bifid, an 
fitting into notches in area of ventral valve. Internal spires ra ‘se 
Position and locality: Throughout the Rockford Shales, 
. Spirifera strigosa Meek. Spirifera macra Meek (1860), Pro- 
