754 Report oF THE State GEOLOGIST. 
These radiate shells may be conveniently subdivided as follows: 
1. Pauciplicati, or those with few low plications; as Spirifer 
radiatus, Sowerby, S. Zudora, Hall, from the Clinton and Niagara 
faunas, S. macroplewra, Conrad, from the Lower Helderberg 
group. 
2. Multiplicati, or those with numerous plications; as Spurifer 
Niagarensis, Conrad, S. asperatus, Ringueberg, of the Niagara 
group; S. Zullia, Hall, of the Hamilton fauna; S. Belphegor, 
Clarke, of the Genesee shales; S. mesastrialis, Hall, of the 
Chemung group. 
3. Dupliciplicati ; a few Upper Silurian species having strong 
dichotomous plications and the filamentous surface stria covered 
with asperities. Such are Spirifer nobilis, Barrande, from the 
étage E,, and the Niagara limestone of Illinois and Wisconsin, 
and S. Schmidti, Lindstrém, from the Gotland limestone. 
Section II. Lamexzosr. (Plate 24, figs. 1-20.) Typical examples, 
Spirifer perlamellosus, Hall, 8. mucronatus, Conrad. 
Radially plicated; surface covered with numerous concentric 
lamella. In Silurian species the fold and sinus are non-plicate ; 
the later forms usually bear a low median depression on the fold 
accompanied by a corresponding median ridge in the sinus. 
The lamellose species are conveniently subdivided into two 
groups: 
1. Septati; those having a median septum in the pedicle- 
valve. The septum lies between the bases of the teeth, but does 
not come into contact with them as in the genus Crrqa, where 
the latter are supported by dental lamellz resting on the bottom 
of the valve. 
This character is found in’ an incipient condition of develop- 
ment in the Niagara species Spirifer sulcatus, Hisinger, and is a 
more conspicuous feature in subsequent forms, S. perlamellosus, 
of the Lower Helderberg, S. raricosta, of the Upper Helderberg, 
S. consobrinus, of the Hamilton group, and S. mesacostalis, of 
the Chemung group. Up to the period of the Upper Devonian, 
at least in American faunas, the existence of this septum in the 
pedicle-valve is not accompanied by a punctation of the shell- 
tissue nor by the union of the processes on the primary lamelle 
of the spiral arms. 
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