14 PALEONTOLOGY OF NEW YORK. 



rad, from the Lower Helderberg group. Though this type is not abundantly 

 developed in American faunas it embraces a very considerable number of the 

 many forms described by Barrande* from the Bohemian ctages E and F. 

 Among these species the cardinal area has but an incipient development or may 

 be altogether absent, while the dental plates are frequently quite pronounced. 



2. MuUiplicati, or those with numerous plications; as Spirifer Niagarensis, 

 Conrad, S. asperatus, Ringueberg, of the Niagara group ; S. Tullia, Hall, of the 

 Hamilton fauna; S. Belphegor, Clarke, of the Genesee shales; S. mesastrialis, 

 Hall, of the Chemung group. In this group, with the more extended hinge 

 and more abundant plications characterizing the Devonian and Carboniferous 

 Spirifers generally, the radiate type of superficial structure has been maintained 

 the longest. It is evident from material before us, that the type was continued 

 into the faunas of the Lower Carboniferous. 



3. Duplidplicaii. A few upper Silurian species have strong dichotomous 

 plications and the filamentous surface striae covered with asperities. Such are 

 Spirifer nobilis, Barrande, from the etage E^, and the Niagara limestone of 

 Illinois and Wisconsin, and S. Schmidti, Lindstrom, from the Gotland lime- 

 stone. 



The Radiati generally may be said to have prevailed at an early period in 

 the history of the genus. The combination was one that was but little modi- 

 fied during its existence and was involved in no progressive development of 

 generic characters. 



II. Lamellosi. Typical examples, Spirifer perlamellosus, Hall, S. mucrmatus, 

 Conrad. 



TerOn-atula, Atwatbb. Amer. Jour. 8ci. and Arte, vol. ii, p. 224, pi. i, figs. 2, 3. 



Delthyrit, Cokrad. Geol. Survey N. Y., Pal. Uept. ; Fifth Ann. Rept., p. 54. 



Delthyrig, Co.nkad. Jour. Acad. Nat. Sci. Philadelphia, vol. viii, pp. 261, 262, pi. xiv, fig. 18. 



DelthyrU, Vahdxbm. Geology of N. Y. j Rept. Third Dist., p. 132, fig. 3. 



DtlthyrU. Varuxhm. Geology of N. Y. ; Rept. Third Dist., p. 150, fig. 3. 



DdlhyrU, Hall. Geology of N. Y. ; Rept. Fourth Dist., p. 105, fig. 4 ; p. 200, fig. 5 ; 



pp. 202, 269, fig. 9 ; p. 270, fig. 5. 

 DelPiyrU, Hall. Geology of N. Y. ; Rept. Fourth Dist., p. 198, figs. 2, 3 j p. 206, fig. .'J2; 



p. 270, fig. 3. 

 (So) 1843. Spirifer, Castblkao. Easai sur le Systfime Silur. de I'Amer. Septentr., pi. xiii, fig. 1. 



" Syslime bUurien du Centra de la Bobeme, vol. v, pU. i-viii. 



