cragin.] DESCRIPTIONS OF SPECIES. 51 
slope angulated and strongly flattened (radially costate?) ; anterior 
slope a little excavated on the upper part, separated from the outer 
slope by a rounded shoulder, ornamented with a few strongly elevated 
radial costa? separated by comparatively wide intervals, in each of 
which is a feebler linear costella; outer slope flattened, radially cos- 
tate, becoming closely cancellated on the middle and strongly so on 
the ventral part; ventral margin straight, not crenulated. There are 
20 of the costse on the outer slope, small, with their rounded summits 
subgranulated by the cancellation, and separated by intervals of about 
their own width. On the summit of the umbo the axis of flattening 
is inclined forward. 
Measurements. — Height, 10.5 mm.; length, V.) mm.; breadth, 12 mm. 
Occurrence. — One and a half miles east of Malone station; repre- 
sented by only one example. 
The ornamentation of the posterior slope is concealed in the type 
specimen. A radiately costate ornamentation upon it is inferred 
from the fact that the species seems to agree subgenerically with 
Gray's Calloarca as described and figured in Tryon's Structural and 
Systematic Conchology. A slight inequality of the valves in the 
umbonal region is doubtless a distortion due to stratigraphical dis- 
turbance. The specimen does not disclose the characters of either 
the hinge or the ligamental area. 
Arca? dumbli sp. n. 
PL VI, fig. 6. 
Shell small, only moderately inflated, rather elongate-trapezoidal, 
the anterior side short and subvertically truncate, the posterior long 
and obliquely truncate; the base gently convex; the moderately ele- 
vated beaks situated at the rear limit of the anterior third; anterior 
slope small, concave, wing-like, with supero-anterior corner nearly 
ti right angle, separated from the outer slope by a posterior umbonal 
ingulation, which becomes obsolete distally; posterior slope concave. 
3ej:>arated from the outer by a strong, proximally subacute, distally 
obtuse shoulder-like angulation, the two apposed concave slopes 
forming together a sort of wing with obtuse corner; the anterior 
dope ornamented with a few narrow, distally obtuse radial folds, 
I he outer slope with ordinary and strong concentric growth-lines, 
adial lines, if originally present here, having been feeble and oblit- 
erated by weathering in the types, the posterior slope and the summit 
f its limiting angle having numerous radiating raised lines and stria?. 
Measurements. — Height, 16.5 mm.; length, 30 mm.; breadth, about 
2 mm. 
Occurrence. — One and a half miles east of Malone station; repre- 
iiii ented by 5 specimens. 
