26 
SILURIAN MOLLUSC A. 
Fig*. 23.—Far. COSTULATA. 
Var. ft Costis concentricis majoribus, angulatis. 
W e have only tlie posterior half of a shell with so much 
coarser ribs than the other, that many would be disposed to 
consider it distinct. But the shape of the posterior end is 
nearly the same. And the ribs, though coarser, have much of 
the same character as those of the species above described. 
They are angular, prominent ridges, not set quite at equal 
distances, but nearly so. 
Locality .—Same as above. 
BRACHIOPODA. 
As usual, these are the most abundant shells of the Silurian 
deposit. Under generic forms familiar to every student of 
the older rocks, and (although identical with none of them) 
representing even the comiqon species of Wales and Shrop¬ 
shire, they stamp the formation as accurately as if we could 
trace the connection of the beds themselves. This coinci¬ 
dence of numerous genera—and, so far as we know, of spe¬ 
cific groups peculiar to the Lower Silurian—is very remarkable 
and satisfactory when such remote districts are compared. 
It is a clear and convincing proof of the superior influence of 
the element of time over that of locality in regulating the 
palaiontology of an epoch. 
LINGULA KALI- 
Plate 3, fig. 1. 
L. vix semiuncialis, oblonga, plana nisi per medium depressa, 
lateribus parallelis fronte quadrato. Apex angulo aperto 40°. Super¬ 
ficies absit. 
Not half an inch long, nearly flat (the centre depressed, ob¬ 
long, with a square front and rather obtuse angular apex. 
