290 



HISTORICAL GEOLOGY. 



317). It should be remembered that this is the first 

 introduction of ii family (Ammonite family) which in 

 Mesozoic times became extremely abundant. The family 

 is characterized by the dorsal position of the siphon-tube 

 and the complexity of the suture. We shall hereafter 

 trace the increasing complexity of the suture. It only 

 begins in the Goniatite. 



Crustacea. Trilobites still continue under new forms 

 (Fig. 206), but in greatly diminished number and size. 

 They have passed their prime. 



Insects. Insects are now, and at all previous geologi- 

 cal times have been, closely related to land vegetation. 



FIG. 207. 



FIG. 206. 



FIGS. 206, 207. 206. Devonian trilobite and insect: Dalmania puDetata ; Europe. 

 207. Wing of platephemera antiqua ; Devonian, America. (After Dawson.) 



The first conspicuous land vegetation is found in the 

 Devonian, and in connection with this vegetation are 

 found also the first known insects (Fig. 207). These first 

 insects were most nearly allied to cockroaches and dragon- 

 flies in fact, a connecting link between these orders. 



