CAMBRIAN FAUNAS. 113° 
at the medium line of the shell. In Whitfield’s illustration, however, 
the lines are shown to pass more directly across the shell, as they do- 
in the New Jersey specimens. 
ORTHIS NEWTONENSIS DN. Sp. 
Plate I., Figs. 3-5. 
Description.—Shell biconvex, subquadrangular to subelliptical in: 
outline, the hinge-line a little shorter than the greatest width of the 
shell. Pedicle valve regularly convex, greatest convexity near the: 
beak in the smaller shells, but further towards the front in the larger 
individuals; cardinal area of moderate height, flat, sloping backward 
from the hinge-line at an angle of about 45°. Internally the pedicle 
valve has a more or less prominent, concave, muscular impression, 
about one-fourth as wide as the shell and about as long as wide; it 
is a little elevated above the floor of the valve and is bounded laterally 
‘toward the beak by the short, dental plates. Im some of the older 
shells a narrow, mesial, elevated ridge extends forward from the: 
anterior margin of the muscular impression, becoming broader toward 
the front, but dying out before reaching the margin of the shell. The 
brachial valve is less convex than the pedicle; it is depressed along 
the median line in a shallow, ill-defined, broadly-rounded sinus, which 
becomes more conspicuous as it approaches the anterior margin. In- 
ternally the muscular impression is much smaller than that of the 
pedicle valve; it is elevated above the floor of the valve and resembles 
the impression of the other valve, but is marked by a slight, median 
ridge. The surface of both valves is marked by faint, radiating lines, . 
which are visible on the internal casts, but are too imperfectly pre-- 
served to properly exhibit their characters. There are apparently 
about thirty or forty coste upon a shell of average size, some of which 
are coarser, with two or three finer ones between. 
The dimensions of one of the best-preserved pedicle valves are:- 
length, 7 mm.; width, 8 mm.; convexity, 2 mm. 
Remarks.—This is the commonest species in the fauna at Newton,. 
and occurs, also, at several other localities. It is apparently one of the- 
Orthide, but its generic position is not so easily determined. In 
general form the shell. resembles some members of the genus Dal-- 
manella more closely than any others, but the muscular impressions- 
8 
