1866.1 247 fii*^"- 



In comparing this species with Sj)irifera tcxtus, we find similar 

 conditions, or more properly an extension or amplification of the same 

 features. In that species there is a convex arching pseudo-deltidiuni, 

 though rarely preserved in the specimens. Beneath this there is a 

 concave septum, and upon the inner face of this there is a tubular 

 callosity; or, in other words, the inner laminae of the septum become 

 fistulous, and inclose a cylindrical or subcylindrical space, which ex- 

 tends from the base of the septum to near the apex of the valve.* 

 But more usually the laminae appear to be separated, and extending 

 inwards are recurved, their edges sometimes joining to form a tube, 

 but more frequently perhaps the margin of each one is recurved upon 

 itself, leaving the tube with a slit along the lower side. In some 

 instances, however, these extensions from the inner face of the septum 

 continue to the bottom of the cavity, and joining the external shell 

 leave a quadrangular tube instead of a cylindrical one. 



It is evident from what has been said, as well as from the illustra- 

 tions given, that there is a near approach to this character of S. 

 textus, or an incipient step towards it, in Spirifera alta ; but the 

 type has not become fully developed. We have the concave septum 

 with a semicylindrical callosity on its inner face, but this ridge has 

 apparently remained solid. The concave septum, however, must not 

 be confounded with the pseudo-deltidium : the latter is apparently an 

 independent growth of shelly (or sometimes perhaps scarcely solid 

 shell) matter, forming an exterior plate from the apex of the fissure, 

 covering to a greater or less extent the opening; but apparently not 

 connected with, nor a part of the dental lamellfB or substance of the 

 area, while the septum is an outgrowth or lateral extension of the 

 dental plates. 



In the case of Sipirifera alta, the extension of the septum is so 

 great, that when connected with the general form of the shell, its 

 nearest analogue appears to be Spirifcra textus ; which, so far as I 

 can now determine, is identical with the one described as S. subcus- 

 pidatus in the Geological Report of Iowa. The latter is a carbon- 

 iferous species from the Keokuk limestone, and closely allied to the 

 Spirifera cuspidatus of Europe ; and the Chemung species thus re- 

 minds us of the Carboniferous one, or has a carboniferous aspect. 



If, in its full development, the presence of a septum and internal 

 tube be regarded as of generic value, then we have in Spirifera alta 



* It is upon this feature, or one of similar character, in its full development, 

 that I understand Prof. Winchell proposes to found the Qenus Syringothyris. 



