20 Prof. W. King on Spirifer cuspidatus. 
M‘Coy and Davidson. The former has pointed out the exist- 
ence of a “mesial septum, about one-third of the length in old 
specimens, rather more in small ones,” in the valve now under 
consideration *; and the latter has represented an indication 
of the same part in one of his figures of the speciesT. 
Mypology. 
Mr. Davidson’s fossil cast of the interior of the larger valve, 
from the State of Ohio, which has all the appearance of be- 
longing to Spirifer cuspidatus, displays the muscular impres- 
sions with singular beauty f. 
The principal muscles have been attached to the inner or 
convex surface of the medio-longitudinal hollow, and confined to 
the space between the dental plates (fig. 81). Their impressions 
form a group having a pear-shaped outline, the poimted end 
answering to the apex of the umbone, and the rounded end 
terminating a little more than one-fourth from the free margin 
of the hollow. ‘They are longitudinally separated in their an- 
terior three-fourths by a faint linear depression, d (or raised 
line on the inner surface of the valve), and their posterior 
fourth by a rather prominent irregularly indented ridge, ec, 
which rises from the bottom of the anterior half of a deepish 
longitudinally oval cavity, e (elevation, dbid.). The most ob- 
vious impressions are two, a, a, one on each side of the faint 
linear depression, marked on their posterior half with about 
six longitudinal thickish ribs, intersected transversely or 
obliquely, also more or less complicated and obscured, by a 
number of raised diverging lines. The ribs on the transverse 
median line of the large impressions become once or twice 
divided, giving rise to about sixteen others, which are sharply 
defined: these run straight out, or with a slight curve, over 
the anterior half of the impressions§. Between the large im- 
* British Paleozoic Fossils, p. 426. 
+ British Carboniferous Brachiopoda, pl. 8. fig. 21s. 
{ It is worthy of being specially noted that the specimen has been pre- 
sented to Mr. Davidson, with his usual liberality, by Prof. L. de Koninck. 
I must also take this opportunity of acknowledging the great kindness I 
have received from My. Davidson in my present researches; he has not 
only drawn the figures 80 and 31, but has materially aided me in other 
respects. 
§ At first sight it might be supposed that the two large impressions 
actually represent two pairs, the posterior half being one pair, and the 
anterior half another. Seeing how different the posterior and anterior 
divisions appear, I was of this opinion myself for some time ; but, observ- 
ing that the fine ribs on the latter originated by subdivision from the 
strong ribs on the former, which is quite obvious on the right half (the 
left half in the figure), I felt the distinction was untenable. 
