548 



HISTORICAL GEOLOGY. 



Blastoids, or Bud-crinoids, which, like the typical Cystoids, have no free 

 arms, and usually are pentagonal in form. A species from the Niagara lime- 

 stone of Ohio is represented, without its stem, in Fig. 770. 



771-780. 



176 a 



Braohiopods. — Fig. 771, Leptasna rhomboidalis ; 772, Plectambonites transversalis ; 778, a, Atrypa nodostriata ; 

 774, Meristina (Whitfieldella) nitida ; 775, Anastrophla interplicata ; 776, a, Rhynchotreta cuneata ; 777, a, b, 

 Atrypina disparUis ; 778, a, Orthis biloba ; 779, a, Spirifer Niagarensis ; 780, a, Sp. sulcatus. Hall ; except 

 778, Meek. 



Some of the characteristic Braohiopods of the Niagara group are repre- 

 sented, natural in size, in Figs. 771 to 780 — all very abundant species. 



781-784. 



Lamellibbanohs and Gastropods. — Fig-. 781, Megalomus Canadensis; 782, Avicula emacerata; 783, Platy- 

 • stoma Magarense ; 784, a, Platyceras angulatum. 



LeptoRna rJioviboidalis, Fig. 771, is one of the long-lived species — as 

 it began in the Trenton period and continued on, with little change, 

 through the Devonian. 



