148 



HISTORICAL PALEONTOLOGY. 



and, with an almost equally cosmopolitan range, survives into 

 the Carboniferous period. 



Fig. 97. Atrypa reticularis. Upper Silurian and Devonian of Europe 

 and America. (After Billings.) 



The Bivalves (Lamellibranchiatci) of the Devonian call for 

 no special comment, the genera Pterinea and Megalodon being, 



Fig. 98. Strophomena rhomboidalis. Lower Silurian, Upper Silurian, and 

 Devonian of Europe and America. 



perhaps, the most noticeable. The Univalves (Gasteropods], 

 also, need not be discussed in detail, though many interesting 

 forms of this group are known. The type most abundantly 

 represented, especially in America, is Platyceras (fig. 99), 



comprising thin, wide - 

 mouthed shells, probably 

 most nearly allied to the 

 existing "Bonnet-limpets," 

 and sometimes attaining 

 very considerable dimen- 

 sions. We may also note 

 the continuance of the 

 6 genus Euomphalus, with 



Fig. 99. Different views of Platyceras du- its discoidal Spiral shell. 

 ii'c;:nn, of the natural size. Devonian, Canada. A , rr . , j 



(Original.) Amongst the Heteropods, 



the survival of BdleropJwn 



is to be recorded ; and in the " Winged-snails," or Pteropods, we 

 find new forms of the old genera Tentaculites and Conularia 



