SPIRIFER^ OF THE CHEMUNG GROUP. ' 249 



the opposite valve. The casts of the dorsal valve show the marks of a 

 deeply striated cardinal process and elongate teeth-sockets, while the 

 muscular impressions are sometimes strongly marked. 



This species is known to me only in the condition of casts of the interior, and 

 its usual appearance is illustrated in the figures on Plate XLin, Its general aspect 

 is much like that of the European Sjpirifera cuspidata, Maetin; but there are 

 important differences by which it may be distinguished : these are, the plications 

 on the mesial fold, the larger area of the dorsal valve, and the shorter extension 

 and greater divergence of the dental lamell£e by the sides of the muscular im- 

 pression. Some of these characters, I conceive, are not likely to change to those 

 shown by 8. cuspidata. In the concave septum closing two-thirds of the fissure 

 from above, it resembles that species as described by Prof. M'Coy, who mentions 

 the presence of a "deep-seated pseudo-deltidium."* In one of the figures given by 

 Mr. Davidson and referred with doubt to this speciesf, the cast shows a tubular 

 perforation in the filling of the fissure; and a gutta percha impression from the 

 same shows the mark of a foramen, but there is no positive evidence of a septum 

 which is so conspicuous in our specimens, and which I suppose to be the feature 

 characterized by Prof M'Coy as a deep-seated pseudo-deltidium. In our species, I 

 have not been able to discover any corresponding perforation; the only indication 

 of this being tte semicylindrical impression along the centre of the fissure (in the 

 cast), showing a callosity of the septum behind the exterior wall. 



In form and proportions, this species bears a very close resemblance to one in 

 the Waverly sandstone of Ohio, and also to one in the fine-grained sandstone of 

 Burlington, Iowa; but of neither of these have I the necessary material for satis- 

 factory comparison. It differs from the S. subcuspidataX of ScroruR in the plications 

 on the mesial fold and sinus, and the wider area of the dorsal valve; and also in 

 the same characters it differs from the S. textus of the sandstone and argillaceous 

 limestone near New-Albany, Indiana. 



Geological formation and locality. This fossil occurs in finegrained ferruginous 

 sandstone of the Chemung group, at Meadville, Pennsylvania ; associated with 

 Spirifera disjuncta, S. prcematura, Streptorhynchus chemungensis \ar. pectinacea, 

 Choi'tes muricala, C ?, Productus {^Productella) lachrymosa, etc. 



• • • • • . triangular opening very large, often displaying the internal deep-seated pseudo- 

 deltidium (without perforation, leaving the only opening to the shell at its base); • • •. McCot, 

 British Palaeozoic Fossils, p. 426. 



t Monograph of British Carboniferous Brachiopoda, Plate ix, f. 1 & 1 a. 



X Spirifer aubcuspidaius, Hall, Geological Report of Iowa, pa. 646, pi. 20, f. 6, i$ a distinct species, 

 and apparently identical with S. textus, Hall, Tenth Report on the State Cabinet, p. 160 : 1857. See 

 Nineteenth Report on the State Cabinet, for remarks on this species. 

 [Pal.£ontolooy IV.] 32 



