308 
PALAEONTOLOGY OF NEW YORK. 
to the group, and this fact, taken in connection with its spinous strife, leads to 
the presumption that the interior, when known, will show some generic varia¬ 
tions of more or less importance. 
The earliest appearance of Chonetes in American Palaeozoic faunas, is in the 
Clinton group (C. cornuta, Hall); Chonetes undulata, C. temistriata, C. Novascotica, 
Hall, are known in the Niagara fauna. There is an undescribed species in the 
Lower Helderberg, and at least one other in the Oriskany sandstone of New 
York, but these are of rare occurrence. Billings has described from the Lower 
Devonian (Oriskany horizon) of Gaspe and the Bay of Chaleurs, C. Canadensis 
and C. Antiopia. In the Devonian the species multiplied rapidly, and • then 
attained their maximum development, both in number and size; becoming less 
conspicuous in the following faunas, as the productoids increased in develop¬ 
ment and importance.* 
Whether the cardinal spines are ever absent in true Chonetes is not yet posi¬ 
tively determined; they are often obscure, and as often lost from accidental causes, 
but no satisfactory evidence of their non-existence has been shown in any species 
that can be strictly referred to Chonetes; although Waagen believes that 
they were probably never developed in one of his species from the Salt-Range. 
An analogous structure is exhibited by the species Leptma ? nucleata, Hall,f 
a small, obscure shell, occurring in great abundance in certain outcrops of the 
Oriskany sandstone in New York and Illinois, and in the Upper Helderberg 
chert of Cayuga, Province of Ontario. In contour the shell is concavo-convex, 
and externally is unlike Chonetes in having a smooth surface with concentric 
squamose lines Or lamellae of growth, but no radiating striae, and no spines, 
either on the cardinal margin or over the surface. The delthyrium appears to 
have been uncovered. On the interior the pedicle-valve has a broad, thick and 
considerably elevated median septum, which takes its origin at, or just in front 
of the apex and is continued over about one-third the length of the shell, end¬ 
ing quite abruptly. In well preserved internal casts the impressions of the 
* Waagen observed (1S84), when adding to the genus fourteen new species from the Productus lime¬ 
stone, that only about sixty species had been previously known, according to Zittel. This estimate is far 
too low, since just about sixty well defined species have been described from American faunas alone. 
t Palaeontology of New York, vol. iii, p. 419, pi. xciv, figs. 1 a-d. 
