LAURENTIAN AND EARLY PALEOZOIC. 



29 



Glimactichniies, from the same beds which afford Pro- 

 tichnites. The principal difference between Protichnites 

 and their modern representatives is that the latter hare 

 two lateral furrows 

 produced by the 

 sides of the cara- 

 pace, which are 

 wanting in the for- 

 mer. 



I subsequently 

 applied the same 

 explanation to sev- 

 eral other ancient 

 forms now known 

 under the gener- 

 al name Bilobites 

 (Figs. 6 and 7).* 



The tubercu- 

 lated impressions 

 known as Phyma- 

 toderma and Gaul- 

 erpites may, as Zeil- 

 ler has shown, be 

 made by the bur- 

 rowing of the mole- 

 cricket, and fine examples occurring in the Clinton forma- 

 tion of Canada are probably the work of Crustacea. It is 

 probable, however, that some of the later forms referred 

 to these genera are really Algse related to Caulerpa, or 

 even branches of Conifers of the genus BrachypJiyllum. 



. Nereites and Planulites are tracks and burrows of 

 worms, with or without marks of setas, and some of the 



Fig. 7. — BuaophyeM (RusichnUe») GfrmviUen- 

 sis, an Eiuiinal burrow of the Siliwo-Cam- 

 brian, probably of a crustacean, a, Track 

 connected with it. 



* The name BUobites was originally proposed by De Kay for a bivalye 

 shell (Conocardiitm). Its application to supposed Algse was an error, 

 but this is of the less consequence, as these are not true plants but only 

 anitual trails. 



