210 



PALEOZOIC TIME — LOWER SILURIAN. 



-h 



3. Mollusks — (a.) Bryozoans. — Fig. 266 represents the Betepora incepta, 

 ft thin reticulate coral, the surface of which, magnified, is shown in fig. 266 a; 



Figs. 264-276. 



Radiates. — Fig. 264, Palaeocrimis striatus; 265, Malocystis Murchisoni. Mollusks. — 266, 

 Retepora incepta; 267, Ptilodictya fenestrata; 268, Orthis costalis: 269, Leptasna plicifera; 

 270, Rhynchonella plena; 271, Maclurea magna; 272, M. Logani (X /^); 273, operculum 

 of same; 274, Scalites angulatus; 275, Bellerophon rotundatum. Articulates. — 276, Le- 

 perditia Canadensis, var. nana. 



fig. 267, Ptilodictya fenestrata, a small branching species, covered with minute 

 cells, and fig. 267 a, the surface magnified. 



(b.) Brachiopods. — Fig. 268, Orthis costalis H. ; fig. 269, Leptsena plicifera H. ; 

 L. incrassata H. ; fig. 270, Bhynchonella plena H. (a side-view). 



(c.) Conckifers. — None have been described. 



(d.) Gasteropods. — Fig. 271, Maclurea magna, which is very abundant and 

 sometimes has a diameter of eight inches ; fig. 272, Maclurea Logani, showing 

 the shell closed by its operculum; fig. 273, the operculum in side-view; fig. 27-1, 

 Scalites angulatus Con. ; fig. 275, Bellerophon (Bucania) rotundatum. 



(e.) Ceplialopods. — Orthoceras recti-anmdatum H. ; 0. tenuiseptum H., a large 

 species, with the septa thin and rather crowded. 



4. Articulates — (a.) Trilobites. — Among the species there are Jllsemts 

 Arcturus H. ; i. crassicauda? ; Asaphus obtnsus H. ; Asaphus (Isotelus) gigas 

 (fig. 320). There are also species of Bathyurus and Ampyx in the Canada rocks. 



