274 
BULLETIN OF THE NATURAL HISTORY SOCIETY. 
This species is like L. bellus, Walcott, in form, but is smaller; also 
the growth lines are finer and more sharply defined on the surface of 
the shell. It is proportionately a wider species than L. Billingsiana y 
Whiteaves. 
Lingula (?) lens, n. sp. PL V, figs. 3 a-h. 
Shell substance calcareo-corneous. A broadly ovate species, with 
rather thin, smooth valves, having flattened lateral slopes in the 
ventral valve, and being somewhat tumid toward the umbo in the 
dorsal valve. 
Ventral valves rather blunt at the umbo, whence for about one- 
third of its length the curve of the margin is somewhat straightened, 
for the rest of the border it is regularly rounded to the front ; the 
greatest width is a little in front of the mid-length. The umbonal 
ridge extends about half of the length of the valve, whence to the 
hinge the sides of the valve are flattened ; in front of the middle of 
the valve the slopes are evenly but flatly arched down to the margin. 
Interior . — The position of the central group of muscles is within the 
posterior third of the valve, and the position of the laterals is indicated 
by a bounding ridge ; these features are very faintly marked. 
The dorsal valve is broadly ovate, and its slopes are more strongly 
arched in the posterior half than elsewhere, otherwise it is like the 
ventral. Interior . — This has a sharp, low septem for half its length, 
and on each side a parallel ridge, extending to the middle of the valve ; 
at half the length of these ridges are small lenticular scars, and at 
their outer ends the group of central muscles. The lateral muscles 
form a wide arch at the sides of the valves, opposite the middle of the 
median ridges. 
Sculpture . — The outer (calcareous) crust in this species is normally 
smooth in appearance, but is beset with minute pits. The sculpturing 
of the layer beneath has impressed itself on the outer layer in differ- 
ent parts of the surface ; at the sides and in front we find concentric 
ridges, and in the middle third the imprint of the vascular strise that 
run toward the front margin. These markings are much more dis- 
tinctly shown on the next (corneous) layer. 
Size. — Length of the ventral valve, 15 mm.; width, 13 mm. The 
dorsal valve is 1 mm. shorter than the ventral. 
Horizon and locality. — Thin calcareous layers in the flags of Div. 
3« at McAdam shore, Escasonie, Cape Breton. The shells in these 
