ISO HISTORICAL PALAEONTOLOGY. 



forms of the great genus Producta * itself. In the Devonian 

 period, there is an intermediate state of things, the genus 

 Chonetes being continued in new and varied types, and the 

 Carboniferous Producta being represented by many forms of 

 the allied group Productella. Amongst other well-known De- 

 vonian Brachiopods may be mentioned the two Iong 7 lived and 

 persistent types Atrypa reticularis (fig. 97) and Strophomena 

 rhomboidalis (fig. 98). The former of these commences in the 

 Upper Silurian, but is more abundantly developed in the De- 

 vonian, having a geographical range that is nothing less than 



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

 and America. (After Billings.) 



world-wide; whilst the latter commences in the Lower Silurian, 

 and, with an almost equally cosmopolitan range, survives into 

 the Carboniferous period. 



The Bivalves (Lamellibranchiata} of the Devonian call for 



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

 Devonian of Europe and America. 



no special comment, the genera Pterinea and Megalodon being, 

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

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



* The name of this genus is often written Productus, just as Spirifera 

 is often given in the masculine gender as Spirifer (the name originally 

 given to it). The masculine termination to these names is, however, gram- 

 matically incorrect, as the feminine noun cochlea (shell) is in these cases 

 understood. 



