1847.] SHARPE ON THE PALMOZOIC ROCKS OF N. AMERICA. 177 
each side) ; the ribs are simple but rather irregular ; they decrease in 
size towards the extremity of the wing, at first slowly, so that the 
twelve or fifteen ribs on each side of the middle are nearly equal ; 
beyond those they decrease rapidly and the exterior ribs are very 
small and indistinct. The mesial fold is plain and produced in front, 
the sinus is also plain. The concentric lines of growth are strongly 
marked and very irregular and give a coarse appearance to the shell. 
The hinge-area is large and triangular and marked irregularly with 
strong lines parallel to the hinge; the angle at the apex varies from 
100° to 110° (in S. cuspidatus this angle is about 80°), the apex 
bends over backwards very slightly. The foramen occupies about 
a fourth of the length of the hinge-area in English specimens, but 
only about one-fifth m those from New York. 
Breadth at the hinge 21 inches ; length of the dorsal valve 1+ inch ; 
length of the ventral valve 1 inch; height of hinge-area | inch. 
~ Found at Moscow and on the shores of Seneca Lake in the state 
of New York in rocks of the Hamilton group. In England we find 
this species in the lower beds of the mountain limestone at Kendal, 
and at Barton and S. Petherwin ia the Devonian system. 
The small shell figured by Mr. Phillips as S. cuspidatus, f. 124 (3. 
of the ‘ Palzeozoic Fossils of Devon and Cornwall,’ appears to belong to 
the S. macronotus, with which it agrees in proportion. I refer also 
to the same species M. de Koninck’s S. cuspidatus from the moun- 
tain limestone of Tournay, pl. 14. f. 1, ‘ Fossiles de Belgique’ : the 
general form and size of the shell and the obtuse angle at the apex of 
the hinge-area correspond with S. macronotus, from which it only 
differs in having fewer ribs, less strongly marked concentric lines, and 
a neater and more regular aspect. 
(12) Sprrirer pLicatus.—Two species have been confounded in 
this country under the name of S. octo-plicatus; the original one, 
figured in the ‘ Mineral Conchology,’ t. 562. f. 4, is from the carboni- 
ferous limestone ; this must of course retain the name: the other, 
from the Wenlock limestone of Dudley, figured in the ‘Silurian Sy- 
stem,’ t. 12. f. 7, requires another specific name. 
The latter species is common in the limestone of the Wenlock 
period in the state of New York, where it has been published by Mr. 
Vanuxem under the name of Orthis plicatus, which has been cor- 
rected by Mr. Hail to Delthyris plicatus. Under these circumstances 
we cannot hesitate to adopt the specific name of plicatus for our 
Silurian species, which may be described as follows :— 
Spirifer plicatus ; globose, with a produced and incurved beak ; 
from four to six simple, rounded ribs on each side of the mesial fold, 
which is broad, flattened and divided by a slight longitudinal furrow 
or depression; mesial sinus broad and rounded. Surface entirely 
covered with fine concentric undulating lamine. Hinge-line hardly 
equal to the width of the shell. Hinge-area large and triangular. 
Width 2ths of an inch ; length of dorsal valve Sths of an inch; of 
ventral valve 3ths of an inch. 
Found in England in the Wenlock limestone at Dudley, Wenlock, 
Woolhope, &c., and in the Ludlow formation near Kendal. Found 
VOL. IV.—PART I. P 
