202 



PALEOZOIC TIME. 



form ; and these, although smaller species, were probably of superior 

 rank to the Orthocerata. 



Trilobites (Figs. 360-366), continued to be the most common and 



Crustaceans. — Fig. 360, Asaphus gigas (XK); 361, a, Calymene Blumenbachii ; 362, Lichas 

 Trentonensis ; 363, Trinucleus concentricus ; 364, 365, Agnostus lobatus (X4); 366, same, 

 natural size ; 367, a, b, Leperditia fabulites (natural size). 



largest of Articulates. Besides, there were many of the little 

 bivalve Crustaceans or Ostracoids, the shell of one species of which 

 is shown in Fig. 367. 



Characteristic Species. 



1. Trenton Epoch. 



1. Protozoans. — Sponges. — Astylospongia parvula B. from the Trenton, near 

 Ottawa City, Canada. Perhaps related to the Sponges, Stroinatocerium ruyomm H., 

 Black Biver limestone; and Receptaculites globularis H., R. OweniH.., from the Galena 

 limestone of Wisconsin and Illinois. 



2. Radiates — (a.) Polyps. — Fig. 317, Petraia corniculum H., a coral of the 

 Cyathophyllum family, P. profunda H., Trenton limestone; P. aperta B., Black Biver 

 limestone. Fig. 318, Colwmnaria alveolata H., Black Biver limestone, but occurring 

 elsewhere in the Trenton, — a section of one of the columnar cells shows the tables or 

 partitions of the interior; Fig. 318 a, top-view, showing the radiate cells; Fig. 319, 

 Ckcetetes lycoperdon of the Trenton, a solid coral of a conoidal or hemispherical form, 

 having a fibrous or fine columnar structure, as shown in the sectional view, Fig. 320. 

 Stenopora fibrosa Goldf., is a common species ; it began in the Calciferous, and con- 

 tinued into the Upper Silurian. The chain-coral (genus Halt/sites, a species of which 

 is shown in Fig. 370) is occasionally found in the Trenton rocks, as in the Galena 

 limestone, and in Canada. Fig. 372, Tetradium fbrosum Saff., Tennessee, Canada, a 

 fine columnar coral with tubular quadrate cells; T. columnare H., Tenn. ; Aulopora 

 arachnoidea H. 



(b.) Acalephs. — Fig. 321, Graptolithus amplexicaulis H. of the Trenton, of New York 

 and Tennessee; 321 a, an enlarged view. The genera Chatetes (Fig. 319) and Steno- 

 pora have been referred to the Acalephs. 



(c ) Echinoderms. — Fig. 322, the Star-fish Palceaster matutina H., of the Trenton; 



