8PIKIFERJE OF THE CHEMUNG GROUP. 253 



Spirifera cuspidatiis of Europe; and the Chemung species thus reminds us of the 

 Carboniferous one, or has a carboniferous aspect. 



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

 garded as of generic value, then we have in Spirifera alta the same appendages 

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

 But had we the means of examining the internal characters of the ventral valves 

 of all the species of Spirifcrs, we should probably fiud gradations 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 fissure occupying a narrow space in its apex, till we reach 

 the development observed in 8. alta and S. textus. 



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

 valves of Spirifera radiata of the Clinton and Niagara groujis, there is a filling of 

 the rostral cavity, and a thickening of the dental lamellae which arc 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 filling of the rostral cavity and a 

 thickening of the dental lamellaj, which ai-e distinctly separate, but no appearance 

 of a septum; and there is a low median crest in the muscular impression. 



In the Lower Helderberg group, the Spirifera macroplmra has the rostral 

 cavity filled to a greater or less extent, and the dental plates extremely thickened 

 at their bases; while there is an obscure low median crest in the muscular impres- 

 sion, which sometimes becomes thickened and expanded above; and occasionally 

 there is a little filling of the upper part of the fissure, resembling the incipient 

 stages of growth of the septum. In Spirifera cycloptera the rostral cavity is more 

 or less filled and solid, with diverging dental lamella;; while the crest dividing 

 the muscular impression is very unequally developed, and there is no appearance 

 of a septum. In Spirifera perlamellosa the rostral cavity is filled to a greater or 

 less degree, the dental lamellae are short and strong, and there is a sharp elevated 

 median crest or septum in the muscular impression; but there is no indication of 

 the transverse septum. In Spirifera odocostata the dental lamellje are thickened, 

 and there is a vertical septum reaching from the apex of the rostral cavity to the 

 base of the muscular impression. In Spirifera marylandica of the Oriskany sand- 

 stone, there is sometimes a partial filling of the rostral cavity, with a reversed 

 conical crest in the upper part of the muscular area. Spirifera arenosa has strong 

 dental lamellfe; a filling of the rostral cavity in old shells; a low crest dividing 

 the muscular impression, which ,l5ccomes thickened in its ujiper part; a distinct 

 pseudo-deltidial covering of the fissure, but no transverse septum. 



Among the Spirifcrs of the Upper Helderberg group, Spirifera acuminata has 

 usually only a moderate thickening of the rostral portions, divergent lamellaa of 



