UPPER SILURIAN. 



225 



pods, of which 411, Pentamerus oblongus, is a large and characteristic 

 species, occurring also in the Niagara beds of Illinois, Wisconsin, and 



Fie. 422 A. 



«tt*(H2 





JMm< 



? (Rusophycus) bilobatus. 



Iowa ; 419, a Lamellibranch, of the genus Avicula ; 420, a Gastero- 

 pod, of the genus Cyclonema. Fig. 421 represents a trail, supposed to 

 be that of a Mollusk; and 422, that of a worm (Annelid). 



Fig. 422 A represents a cast common in the Clinton sandrock. It 

 was formerly supposed to be a sea-weed, but is now regarded as the 

 cast of the trail of an Articulate. 



In the Niagara group, among the many corals, there are the follow- 

 ing, here represented. Fig. 423 is one of the Cyathophylloids or cup 

 corals ; 424, one of the Favosites, a columnar coral so named from 



423 



Figs. 423-428. 



Corals. —Fig. 423, Chonophyllum Niagarense ; 424, a, Favosites Niagarensis ; 425, Halysites 

 catenulata ; 426, 427, Heliolites spinipora ; 428, Stroinatopora concentrica. 



favus, a honeycomb, in allusion to its columnar structure (shown in 

 Fig. 424 a) ; 425, a chain coral, or species of Halysites, 428 a Strom- 

 atopora, probably a Protozoan coral, either a calcareous Sponge or a 

 Foraminifer. 



Three of the Niagara Crinoids are illustrated in Figs. 429-431 ; 

 429 shows the cluster of arms at top, which in the living state opened 

 15 



