14 Prof. W. King on Spirifer 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 cuspi- 

 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 desired f. 



As stated in my last communication to the ^ Geological 

 Magazine,' I made known, in 1846, that 8pi7nfer heterocUtus 

 (now Cyrtina heterocUta) 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. alatusj 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" J. 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 di*awing is given of the apophysis, in PL III. fig. 8 ; 

 I have also represented a transverse section of the same part 

 in ^g. 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, ^, 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 sujDposing that Prof. M^Coy 

 has observed the apophysis in Spirifer cuspidatus. He de- 

 scribed, in 1855, the large valve as possessing a " triangular 

 opening very large, often displaying the internal deep-seated 

 pseudo-deltidimn (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 septoms in his genus Cyrtina. He ap- 

 pears to have overlooked the question put in my former commimication 

 as to the type of this genus. 



t See Lamarck's ' Animaux sans Vertebres,' 2nd ed. vol. vii. p. 3G8 

 (1836). Deshayes, referring to the area, states that it '' est traversee dans 

 toute sa hauteur par une gouttiere triangulaire ; si la matiere dure de la 

 couche qui la remplit ordinairement a 6te enlev^e, on trouve cette gout- 

 tiere ferm^e dans presque toute son ^tendue, et offi-ant, vers le sommet, un 

 trou ovalaire, de sorte que cette coquille, malgre I'^trangett? de sa forme, 

 a en effet les caracteres des T^rebratules." 



X Precited Monograph, p. 131. 



§ British Palfeozoic Fossils, p. 426. 



II Proc. Acad. Nat. Sc. Philadelphia, Dec. 18G5, p. 277. 



