W. H. Twenhofel — Silurian Section at Arisaig. 163 



Other common fossils are Pholidops implicata (= Crania 

 acadiensis Hall), Spirifer subsulcatus, S. rugcecosta (a devel- 

 opment out of the previous species and closely related to S. 

 bijugosa McCoy of Ireland, said to be of Wenlock time), Schu- 

 chertella subplana (rare), Phynchonella nucida (a Ludlow 

 guide fossil), Cornidites flexnosus (reappearance of the lower 

 form), Bucanella tvilobata (much larger than those of lower 

 horizons), Grammysia acadica (rather indicative of Ludlow), 

 G. rustica, Goniophora transie?is, Pteronitella venusta, P. 

 curta, Beyrichia pustuloses B. wquilatera, A caste logani, 

 Ccdymene tiibercidata (large), and Homalonotus dawsoni (a 

 flat-headed form unlike any other American species, attaining 

 to a length of about three and one-half inches. One imper- 

 fect specimen of apparently the same form indicates a size of 

 5 inches or more. This species appears in Division II). 



From this evidence Division IVb correlates clearly with the 

 Ludlow. Kiaer cites Megalomus gothlandicus from the Mid- 

 dle Ludlow, and as this fossil occurs in Gotland with Trime- 

 rella, it would appear that Division IYb has its nearest time 

 equivalent in the Guelph of Interior America. 



Along the shore in the upper part of Stonehouse formation 

 Mr. Twenhofel picked up the cast of a ventral valve of a large 

 Spirifer related to S. mcicropleura and S. niagarensis. The 

 specimen is out of a brick-red shale and is as large as the 

 former species but has more plications and is a natter form, in 

 both of which characters it approaches S. niagarensis. This 

 fossil seems to indicate proximity to Helderbergian (New Scot- 

 land) deposits, but as it is not S. macropleura, a form also 

 unknown in the Helderbergian deposits of Dalhousie, New 

 Brunswick, and G-aspe, Quebec, it does not seem wise to lay 

 much correlation value upon it for the present. 



Bibliography. 



1836 Remarks on the Geology and Mineralogy of Nova Scotia (with map). 



Abraham Gesner. Halifax. 

 1845 On the Lower Carboniferous Rocks, or Gypsiferons Formation of Nova 



Scotia. J. W. Dawson. Quar. Jour. Geol. Soc. London, vol. i, pp. 



30-31. 

 1850 On the Metamorphic and Metalliferous Rocks of Eastern Nova Scotia. 



J. W. Dawson, Quar. Jour. Geol. Soc. London, vol. vi, pp. 347-364. 

 1855 Acadian Geology. J. W. Dawson, 1st ed., London, p. 315. 



1859 On the Fossiliferous Rocks of Arisaig. D. Honeyman, Trans. Lit. and 



Sci. Soc. of Halifax, pp. 19-29. 



1860 Description of a new Paleozoic Starfish of the Genus Palaeaster from 



Nova Scotia. E. Billings. The Canadian Naturalist and Geologist, vol. 



v, pp. 69-70. 

 1860 On the Silurian and Devonian Rocks of Nova Scotia. J. W. Dawson, 



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vol. v, pp. 144-159. 



