IOO NEW YORK STATE MUSEUM 



narrower and greatly produced. This latter feature is one of the distin- 

 guishing characters of the species. 



The septa are slightly but regularly concave, the camerae quite shallow. 

 The siphuncle is ventral and almost marginal on the earlier septa ; its posi- 

 tion on later septa has not been observed. The surface, not heretofore 

 noted, is ornamented by quite regular, low, broad, concentric ridges sepa- 

 rated by narrow interspaces. These make a broad backward curve on the 

 venter, bend upward at the sides, and on the dorsum make a sharply angu- 

 lar, posterior curvature. At the aperture they are not parallel to or concen- 

 tric with the margins. 



Dimensions. A specimen nearly entire to the apex has a length of 

 50 mm, the greatest diameter (living chamber, not including apertural 

 extensions) being 28 mm. 



Locality. Upper Guelph horizon, Rochester. 



thochockbas Barrande. 1847 

 (sphvkadockbas Hyatt) 



Trochoceras desplainense McChesney 



Plate 20, fig. 3-9 



Trochoceras desplainensis McChesney, New Paleozoic Fossils. 1859. 



p. 68, pi. 6, fig. 1 

 Trochoceras desplainense Hall, N. Y. State Cab. 20th An. Rep't. 1867. 



p. 359, pi. 16, fig. 8, 9, 10 

 Trochoceras desplainense Whiteaves, Paleozoic Fossils. 1884. v. 3, pt 1, 



p. 36, pi. 5, fig. 5 

 Trochoceras desplainense Whiteaves, Paleozoic Fossils. 1895. v. 3, pt 2, 



P- io 5 

 The specimens which we identify with this species are of better quality 

 than those which have heretofore been figured and studied, one of them 

 retaining almost in its entirety the living chamber and aperture, another of 

 somewhat smaller size preserving the umbilical aspect of the entire final 

 whorl to the aperture, while still other specimens illustrate the grosser and 

 finer characters of the early surface. 



