UPPER SILURIAN. 



227 



Figs. 448 to 451 represent some of the Niagara Trilobites ; 449 is 

 one third the actual length, and 450 a fourth, the latter attaining some- 

 Figs. 444 A-447. 



445 



J«a«ellibranchs and Gasteropods. — Fig. 444 A, Megalomus Canadensis; 445, Avicula emacerata; 

 446, Platyostoma Niagarensis ; 447, a, Platyceras angulatum. 



Figs. 448-452. 

 449, 



Crustaceans. — Fig. 448, Dalmanites limulurus {XX)] 449, Lichas Boltoni (XX); 450, Homa- 

 lonotua delphinocephalus (XK)\ 451, Illsenus Barriensis ( X %) ; 452, Beyrichia symmetrica ; 452, 

 a, same, natural size. 



times a length of a foot. In Fig. 448, the eyes are very large, and in 

 450, small. Fig. 452 is a side view, enlarged, of an Ostracoid or bi- 

 valve Crustacean. Another group of Crustaceans, the Phyllopods, 

 were represented by species of the genus feratiocaris, having, as 

 shown in Fig. 484, on page 247, the general form of a Shrimp. 



