290 REPORT ON THE STATE CABINET. 



valve.* But more usually the lamiua3 appear to be separated, and, extending 

 inwards, are recurved, their edges sometimes joining to form a tube; but more fre- 

 quently, perhaps, the margin of each one is recurved upon itself, leaving the tube 

 with a slit along the lower side. lu some instances, however, these extensions 

 from the inner face of the septum continue to the bottom of the cavity, and, join- 

 ing 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 illustrations 

 given, that there is a near approach to this character of S. textus, or an incipi- 

 ent step towards it, in Spirifera alta ; but the feature has not become fully 

 developed. We have the concave septum with a semi-cylindrical callosity on 

 its inner face, but this ridge has apparently remained solid. The concave 

 septum, however, must not be confounded with the pseudo-cleltidium: 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 

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

 connected with, nor a part of the dental lamellae or substance of the area, 

 while the septum is an outgrowth or lateral extension of the dental plates. 



" In the case of Sjnrifera alta, the extension of the septum is so great, that 

 when connected with the general form of the shell, its neatest analogue appears 

 to be 8j)irifera textus ; which, so far as I can now determine, is identical with 

 the one described by me as 8. subcimpidatus in the Geological ltej)ort of Iowa. 

 The latter is a carboniferous species from the Keokuk limestone, and closely 

 allied to the Spirifera cuspidatus of Europe; and the Chemung species thus 

 reminds us of the Carboniferous one, or has a cai'boniferous aspect. 



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

 regarded as of generic value, then we have in Spin/era alta the same append- 

 ages in part, or in a partially developed condition; the distinct tube only being 

 wantiuo-. But had we the means of examining the internal characters of the 

 ventral valves of all the species of Spirifers, we should probably iind grada- 

 tions from the solid filling of the rostral cavity, with a greater or less extension 

 of shelly matter in the form of a septum in the tissure occupying a narrow 

 space iu its apex, till we reach the development observed in 8. alta and S. textm. 



"To a considerable extent, we are able to prove this supposition. In the 

 separated valves of 8pirifera radiata of the Clinton and Niagara groups, there 

 is a tilling of the rostral cavity, and thickening of the dental lamellae which 

 are extended for half the length of the valve. The narrow median crest of 

 the muscular impression is expanded and thickened towards the apex of the 

 valve, but there is no evidence of a septum. In Spirifera niagarensis there is 

 a tilling of the I'ostral cavity and a thickening of the dental lamellae, which 

 are distinctly separate, but no appearance of a septum; and there is a low 

 median crest in the muscular impression. 



" Iu the Lower Helderberg group, the 8pirifera macropleura has the rostral 

 cavity tilled to a greater or less extent, and the dental plates extremely thick- 

 ened at their bases; while there is an obscure low median crest iu the muscular 

 impressions, which sometimes becomes thickened and expanded above; and 



* It is upon this feature, or one of similar cliaracter, in its full development, that I understand 

 Prof. WiNCHELL proposes to found the Genus Stringothtris. 



