SPIRIFERIDiE. 



105 



narrow space for the passage of a pedicle, for the protrusion of which a minute foramen is 

 sometimes observed in the beak. From the sides of this process, above the junction of 

 the teeth of the opposite valve, and at the point where it bends upwards, originate the 

 criu-al processes which support the spires. A deep cavity beneath the cardinal process 

 extends to the dorsal beak, from which originates a thin elevated septum, running to the 

 base of the shell. Muscular imprints confined to a narrow oval space. Surface apparently 

 smooth ; under a lens, punctate ; shell-structure dotted, and, when perfect, covered with 

 minute hair-like spines. 



" Observations. In Murchison's ' Silurian System,' Mr. Sowerby has described, under 

 the name Sjnrifer ? pisum, a species differing essentially in general external characters 

 from the typical forms of that genus. This species has been adopted as a true Spirifer in 

 Morris's ' Catalogue of British Fossils,' and in the ' Nomenclator Palaeontologicus ' of 

 Bronn, as well as elsewhere. Subsequently I discovered in the Niagara Shales a form so 

 similar to the British species that I regarded it as identical; but from the condition 

 and character of the specimens, I considered them as more nearly allied to Orthis than 

 to Spirifer, and, accordingly, in the Second Volume of the ' Palaeontology of New York,' 

 I designated the Niagara fossil ' Ortliis pisvni! 



" Since that period my collections from the Helderberg have revealed a species similar 

 to the one from the Niagara group ; but among the numerous individuals from the latter 

 rocks, I found several which were clearly furnished with internal spires like the true 

 Spirifer, thus separating it from Orthis by unequivocal characters. Finding no genus 

 for the reception of these forms, I described the latter as Spirifer ventricosus ; and it has 

 been so published in my Descriptions of New Palaeozoic Fossils in the 'Report of the 

 Regents of the University upon the State Collections of Natural History.' 



" Further examination has satisfied me of the impropriety of placing this fossil under 

 either of the genera named, for several reasons. The central depression, line, or narrow- 

 sinus, which might be regarded as the mesial sinus of Spirifer, is almost equally a 

 character of both valves. The apparent area is not a true area ; and the apparent fora- 

 men, being merely a depression in the false area, does not correspond to the foramen 

 either of Spirifer or of Orthis, not opening into the cavity of the shell. The hinge-hne is 

 not extended in the manner of these shells, particularly of the former ; while the presence 

 of a spire sufficiently distinguishes it from the latter. 



" The lower Helderberg group furnishes one, and perhaps two other species ; and I 

 find that the fossil described by me as Atrypa concinna in the ' Report of the Fourth 

 Geological District' (1843) is another species belonging to the same group of fossils, hi 

 which both the external characters and internal structure difier so essentially from any of 

 the described genera of Brachiopoda as to constitute a distinct genus, and which, from 

 the general nucleolar character of the known species, I propose to designate Nucleospira." 



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