308 PALEONTOLOGY OF NEW YORK. 



to the group, and this fact, taken in connection with its spinous striae, 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) ; Cho?ietes undulata, C. tenuistriata, 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 Gaspc- 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 Leptana ? nudeata, 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 iio 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 



* Waaoen observed (1884), when adding- to the genus fourteen new species from the Productus lime- 

 stone, that only about sixty species had been previously known, according to ZirrKi,. This estimate is far 

 too low, since just about sixty well defined species have been described from American faunas alone. 



t PaliEontolog-y of New York, vol. iii, p. 419, pi. xciv, figs. la-d,. 



