LAUKENTIAN AND EARLY PALAEOZOIC. 



37 



fronds smooth and slightly striate longitudinally, with 

 curved and interrupted striae. Stem thick, bifurcating, 

 the divisions terminating in irregularly pinnate fronds, 

 apparently truncate at the extremities. The quan- 

 tity of carbona- 



ceous matter pres- 

 ent would i ndicate 

 thick, though per- 

 haps flattened, 

 stems and dense 

 fleshy fronds. 



The species 

 Buthotrephis sub- 

 nodosa and B. 

 flexuosa, from 

 the Utica shale, 

 are also certain- 

 ly plants, though 

 it is possible, if 

 their structures 

 and fruit were 

 known, some of 

 these might be 

 referred to differ- 

 ent genera. All 

 of these plants 

 have either car- 

 bonaceous matter 

 or produce organ- 

 ic stains on the 

 matrix. 



The organism 

 with diverging 



wedge-shaped fronds, described by Hall as Sphenothallus 

 angustifolius, is also a plant. Fine specimens, in the 

 collection of the Geological Survey of Canada, show dis- 



Fig. 13.- 



-Buthotrephis Grantii, a genuine Alga 

 from the Silurian, Canada. 



