20 Prof. W. King on Spirifer cuspidatiis. 



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 species f. 



Myology. 



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 cuspidatuSj displays the muscular impres- 

 sions with singular beauty J. 



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. 31) . Their impressions 

 form a group having a pear-shaped outline, the pointed 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, c, 

 which rises from the bottom of the anterior half of a deepish 

 longitudinally oval cavity, e (elevation, ihid,). 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 Palaeozoic Fossils, p. 426. 



t British Carboniferous Brachiopoda, pi. 8, fig. 21 s. 



i 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 Mr. Davidson in my present researches ; he has not 

 only drawn the figures 30 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 difi^erent 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. 



