472 



HISTORICAL GEOLOGY. 



pulchella Billings, is common in the red sandrock of Highgate Springs, Vt.^ 

 and the Winooski marble. Fig. 530 is the same. The very slender species, 



521-526. 



521. 



522. 



523 a. 



r)23. 



MOLLUSKS. — Lamellibranchs : Fig. 521, Fordilla Troyensis (enlarged) ; 521 a, id., cast of interior; 522, Mo- 

 dioloides priscus, very much enlarged. Gastropods : 523, Scenella reticulata; 523 o, prolile as seen in side 

 view showing the height and outline of the conical shell ; 524, Scenella retusa, side view (3) ; 524 a, same, 

 upper view ; 525, Stenotheca (?) rugosa, view from ahove (1); 525 a, 525 6, same, side views; 526, Platy- 

 ceras primsevura, cast (4). Figures from Walcott ; 524, 524 a, after Ford. 



Fig. 531, from Troy, is the type of the genus HyoUthellus of Ford. Fig. 532 

 is the operculum of HyolWies impar. 



527-532. 



527. 



528 a. 



527 a. 



528. 



mj 



529. 



529 a. 



529 6. 



530. 



531. 



532. 



Pteropods. — Fig-. 527, Hyolithes princeps (1); 527 «, outline of cross-section; 528, H. Amerlcanus (2); 

 528 a, operculum of same ; 529, 530, Salterella pulchella ; 529 b, cross-section ; 531, Hyolithellus micans (1) ; 

 532, the operculum of Hyolithes impar. Walcott. 



