Hall.l 



254 ^^^^• 



" 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 

 xliii. Its general aspect is much like that of the European Spi- 

 rifera cuspidata, Martin j 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 lamellae by the sides 

 of the muscular impression. Some of these characters, I conceive, 

 are not likely to change to those shown by S. cuspidata. In the 

 concave septum closing two-thirds of the fissure from above, it re- 

 sembles that species as described by Prof. McCoy, 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 species,t 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. McCoy 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 the semi-cylindrical 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 satisfactory comparison. It differs from 

 the S. suhcuspidataX of Schnur in the plications of the mesial fold 

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

 same characters it differs from the *S'. iextus of the sandstone and 

 argillaceous limestone near New Albany, Indiana."! 



* ; triangular opening very large, often displaying the internal 



deep-seated pseudo-deltidium (without perforation, leaving the only opening to 

 the shell at its base) ; . • • McCoy, British Palaeozoic Fossils, p 426. 



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



X Spirifer subciispidatus, Hall, Geological Report of Iowa, p. 646, pi. xx, f. 6, 

 is 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. 



§ The latter species before alluded to as a punctate shell has the fissure partially 

 closed by a septum, and this is perforated near its apex by a circular foramen, 

 which is continued in a longitudinal tube behind the septum and opens into the 

 cavity of the shell below. The margins of the fissure are grooved for the recep- 

 tion of a pseudo-deltidium as in ordinary spirifers, and this appendage is partially 

 preserved in some of my specimens. 



