75 



noticed therein as were previously described by me. The wide difference 

 between us is due partly to the diversity of opinion as to the specific 

 value of minute characters which must always exist among naturalists and 

 partly to the unsettled state of the generic nomenclature of the Brachio- 

 poda. Such points can only be adjusted by the mutual concurrence of the 

 majority of palseontologists. I think that, at all events, some of the above 

 specific names should be changed as they are pre-occupied by the follow- 

 ing: 



Leptagonia semiovalis McCoy, Strophomena ventricosa, Hall, S. 

 geniculata, id., S. arcuata, id., Orthis ceqidvalvis Hall & Davidson, 0. 

 alata, Salter, Atrypa impressa, Hall, Spirifer tenuistriatus, Hall. 



General Observations on the Paleozoic Fossils op Anticosti. 



1. Lower Silurian. 



In the Lower Silurian rocks of Anticosti there have been collected 121 

 species of fossils, of which the proportionally large number of 85 have 

 been described m this and other pubUcations of the survey as new forms. 

 The remaining 36 are mostly of the common and widely distributed species 

 of the Lower Silurian of Canada West, New York and other countries. 

 They are the following : 



Stenopora, fibrosa, S. mammulata, S. papillata, S. explanata, Halysites 

 catenulatus, Lingula quadrata, Trematis Ottawaensis, Strophomena imbrex 

 S. subtenta, S. planumbona, S. alternata, Lept^ena sericea, Orthis test- 

 udinaria, 0. subquadrata, 0. lynx, Rhynchonella capax, R. recurv- 

 irostra, Ambonychia radiata, Subulites Richardsoni, Trochonema umbil- 

 cata, Pleurotomaria Americana, P. Helena, P. subconica, Murchisonia 

 gracilis, M. ventricosa, Bellerophon acuta, B. bilobatus, Pterotheca 

 transversa, Oncoceras constrictum, Asaphus platycephalus, A. megistos, 

 Dalmanites callicephalus, Cheirurus pleurexanthemus, Harpes Ottawaen- 

 sis, Calymene Blumenbachi, Leperditia Canadensis. 



There are no species which are exclusively Upper Silurian ; the aspect 

 of the whole fauna is eminently Lower Silurian. The rocks are very fos- 

 siliferous throughout, but on approaching the dividing line between this 

 group and Division 1 of the Anticosti group, which immediately succeeds, 

 no less than 80 out of the 121 species suddenly disappear and are seen no 

 more. It is evident, therefore, that there is here a break of considerable 

 importance, probably, in some way connected with the great gap that 

 occurs between the Hudson River and Clinton formations in Canada West 

 and New York. Of the 41 species that pass this break, 30 appear to 

 have become extinct during the period of the deposition of Division I, at 

 least they have not yet been detected in Division 2. Of the remaining 

 e.leven species, seven pass upwards into Division 3, and six into Division 4. 



