NIAGARA GROUP. 



261 



size than that of the Niagara group ; the cardinal area is proportionally smaller, and the hinge- 

 line less extended ; likewise the ventral valve is always more or less convex, particularly in the 

 upper part, while in very rare instances the Niagara species has the ventral valve a little convex. 

 The dorsal valve also of the Niagara species is much more arcuate than the other species, and 

 the surface is marked by fewer strise. 



The Niagara species is extremely rare, so far as we at present know ; while the species of 

 the shaly limestone is extremely abundant, not less than fifty thousand specimens having been 

 collected in a single locality within a few years. 



Fig. 1 a, b. Ventral and dorsal view, where the extremities of the hinge-line are scarcely ex- 

 tended. 

 Fig. I c, d. Another specimen, where the extremities of the hinge-line are auriculate. 

 Fig. 1 e. Front view of a specimen, showing the bilobate character. 



Fig. 1 /, g. Profile views of two specimens, one of which is much more convex than the other. 

 Fig. 1 h, i. Enlarged figures of a specimen, representing the prevailing form. 

 Fig. 1 k. Interior of the ventral valve. 



Position and locality. In the shale of the Niagara group at Wolcott, and rarely at Lockport. 



622. 5. SPIRIFER SULCATUS. 



Pl. LIV. Fig. 2a- /t. 



Delthyris sulcatus. Hisinger, Petref. Suecica, 1837, pag. 73, pl. xxi, fig. 6. 

 Terebratula. Hisinger, Anteckn. v, tab. iii, fig. 2. 



Spirifer octoplicatusl . Sowerby : Murchison, Sil. System, 1839, pag. 624, pl. 12, fig. 7. 

 Delthyris rugatina. Conrad, Jour. Acad. Nat. Sciences, 1842, Vol. viii, p. 261. 

 Delthyris decemplicatus. Hall, Geol. Rep. Third District, 1843, pag. 105, fig. 4. 

 Not Spirifer plicatus*, Sharpe (^Orthis plicatus, Vanuxem ; Delthyris plicatus, Hall), 

 Quart. Jour. Geol. See. London, no. 15, p. 177. 



Shell subtriangular, gibbous ; valves subequal ; cardinal line more or less extended, often 

 mucronate at the extremities ; surface plicated ; plications four to seven on each side of the 

 mesial fold and sinus, crossed by strong imbricating lamellae, and longitudinally marked by 

 fine strise which are interrupted by the edges of the lamellae ; mesial fold of the dorsal valve 

 very deeply impressed towards the base of the shell. 



This species is readily distinguished by its roughly lamellate or rugose surface, which is 

 usually preserved in a tolerable degree of perfection. The only species of the same period 

 which approaches it in character is the S. crispus, which has an evenly striated surface, and 

 less prominent plications. There is a species in the shaly limestone of the Helderberg which 

 possesses the characters of this species even in a higher degree, but the shell is much larger, 

 and very robust. A comparison of the Niagara species with Swedish specimens of S. sulcatus 



* This species is quite distinct from the S. sulcatus, and is restricted to the tentaculite limestone or water-lime, 

 and the lower part of the Pentamerus galeatus limestone, in New- York, being separated from the Niagara group by 

 the entire thickness of the Onondaga-salt group. 



