14 Prof. W. King on Spiriter cuspidatus. 
median plate, extending from the crown of the arch to the 
inner surface of the pertaining valve*. 
Possibly the process was next discovered in Spirifer cuspt- 
datus by M. Deshayes, though I admit that his description of 
what may be taken for it, in his general observations on the 
species, is not so clearly to the point as could be desiredf. 
As stated in my last communication to the ‘Geological 
Magazine,’ I made known, in 1846, that Spirifer heteroclitus 
(now Cyrtina heteroclita) has an arch-shaped process supported 
by a median plate. It also fell to my lot to show, in 1850, that 
a similar structure occurs in a typical Spirifer, the Permian 
Sp. alatus, Schl. My diagnosis of this species states that its 
“dental plates are small, curving, and coalescing ;” and I 
mentioned, in the general observations, that they “have an 
unusual form, being small, curving, and coalescing at their 
upper part, so as to become arch-shaped”’ f. As the original 
figure which I gave of this structure is not sufficiently clear, 
in consequence of its representing a portion of the matrix, 
a fresh drawing is given of the apophysis, in Pl. III. fig. 8; 
I have also represented a transverse section of the same part 
in fig. 9, as exposed by grinding down the umbone of the 
large valve. It will be seen that the process is formed by the 
dental plates, 6, curving in towards each other, and by the 
deposition of shelly matter, c, between them. Although the 
latter fills up the umbonal cavity to a great extent, which is 
not the case in a number of other Spirifers, the dental plates 
are still discernible, passing on and becoming attached to the 
inner surface of the pertaining valve. 
There are some grounds for supposing that Prof. M‘Coy 
has observed the apophysis in Spirdfer cuspidatus. He de- 
scribed, in 1855, the large valve as possessing a “ triangular 
opening very large, often displaying the ¢nternal deep-seated 
pseudo-deltidium (without perforation, leaving the only open- 
ing to the shell at its base)’”’§. Mr. Meek appears to take the 
structure I have italicized for the transverse septum||; but 
* Mr. Davidson places Spirifer septosus in his genus Cyrtina. He ap- 
pears to have overlooked the question put in my former communication 
as to the type of this genus. 
+ See Lamarck’s ‘Animaux sans Vertébres,’ 2nd ed. vol. vil. p. 368 
(1886). Deshayes, referring to the area, states that it “est traversée dans 
toute sa hauteur par une gouttiére triangulaire ; si la matiére dure de la 
couche qui la remplit ordinairement a été enlevée, on trouve cette gout- 
tiére fermée dans presque toute son étendue, et offrant, vers le sommet, un 
trou ovalaire, de sorte que cette coquille, malgré l’étrangeté de sa forme, 
a en effet les caractéres des Térébratules.” 
{ Precited Monograph, p. 131. 
§ British Palzeozoic Fossils, p. 426. 
|| Proc, Acad. Nat. Se. Philadelphia, Dec. 1865, p. 277. 
