Acrotreta in Lower Palaeozoic Shales. 147 



In the St. John Group (Middle Cambrian),' of New Brunswick, 

 Acrotreta trans versalis, Hartt sp. occurs^ which form, belonging 

 to the A. sagittalis group, is strikingly like the Victorian species, 

 •except in surface ornament. 



Summary. 



The group to which the present species is closely allied is 

 Middle Cambrian in America (St. John Group), and Middle and 

 Upper Cambrian (Menevian and Tremadoc) in Wales. Further 

 light is thus thrown upon the homotaxial relationship of the Vic- 

 torian lowest palaeozoic strata with that of other widely separated 

 ^reas, by the discovery of the. above fossils, and in view of the 

 results of the recent examination by the Avriter, of the Heathcotian 

 fauna, there is perhaps little, if any doubt, that these Heathcotian 

 beds should now be regarded as of Upper Cambrian age. Since 

 the Heathcotian has already been shown hx Professor Skeats^ to 

 form one continuous series with the Lower Ordovician (Lance- 

 fieldian), it is now more difficult than ever to draw a distinct line 

 between the Uppei- Cambrian and the Lower Ordovician in Vic- 

 toria, and the occurrence of the form of Acrotreta herein described 

 from Lancefield goes fui'ther to show that, in the Lancefieldian it- 

 self, as is well known, a fair number of Cambrian fossil types co- 

 existed with Ordovician forms. Thus, Clinograptus tenellus is 

 ■Cambrian in some beds elsewhere, Bryograptns is Cambrian in 

 Europe and both Upper Cambrian and Lower Ordovician in New 

 York State, whilst the oldest species of Tetragrajitus seem to 

 represent the transitional zones between Cambi-ian and Ordo- 

 vician. 



In conclusion, I wish to express my thanks to Mr. R. A. Keble 

 for confirmatory evidence regarding the distribution of the grap- 

 tolites. 



EXPLANATION TO PLATE XXVI. 



Fig. 1. — Acrotreta antipodum, sp. nov. Exterior of ventral valve. 

 Probably Heathcotian. Mount William district, x 10. 

 ,, 2. — Ditto. Surface ornament, enlarged, x 30. 



1 OholHla transversa, Hartt. Bull. U.S. Geol. Snrv., No. 10, 1868, p. 644, pi. i., fi^'. 5.5a. 

 Linnarssonla transverm, Hartt sp. G. F. Matthew, Trans. R. Soc. Can., vol. iii., sect, iv., 1885, 

 p. 35, pi. v., figs. 11, lla-e. 



2 " On the Evidence of the Origin, A^e and Alteration of the Rocks near Heathcote, Vic- 

 toria." Proc. Ro}'. Soc. Victoria, vol. xxi. (n.s.), pt. i., 1908, p. 302. 



5a 



