Reviews — Br. C. Barrois — Faune du Gres Arnioricain. 127 



figured and described in the pages of the Geological Magazine 

 several species of Lingida from the same horizon. A few other 

 fossils, Mollusca principally, were also known in these beds ; but 

 owing to the fact that these forms were in poor preservation, 

 existing only as moulds, no systematic attempt had been made to 

 determine them. In spite of this obstacle Dr. Barrois has suc- 

 oeeded in working out this group, and has described and figured 

 in this memoir no fewer that 29 species of Lamellibranchs, 13 of 

 which are new forms. The principal genera represented are 

 Actinodonta, Phillips ; Lyrodesma, Conrad ; Bedonia, Rouault ; Cteno- 

 donta, Salter ; Nuculites, Conrad ; Niicidana, Link ; Oyrtodonta, 

 Billings ; Modiolopsis, Hall, and Hippomya, Salter. The Gasteropoda 

 ^re included in Palceacmoea, Hall, and Bucania, Hall, and there is 

 a single species of Conularia. There are also some Crustacea referred 

 to Myocaris, Salter ; Ceratiocaris, M'Coy, and Trigonocarys, gen, nov. 

 Specimens of the peculiar fossil Discophylium (Actinophyllum) plicatum, 

 Phillips, sp., also occur in the gres armoricain, and they are ranked 

 by the author as calcareous sponges, similar to those of the family 

 Pharetrones, Zittel ; but after a cai'eful examination of Phillips' 

 types, we fail to recognize any characters which can ally them to 

 sponges. 



Including forms previously known. Dr. Barrois now enumerates 

 a list of 45 species of invertebrate fossils from the ' gres armoricain ' 

 in the departments of Ille et-Vilaine and Loire Inferieure. 



Taking into account the occurrence of the genera Ogygia and 

 Homalonotus, and of the Lamellibranchiata now described, the author 

 is fully justified in concluding that the fauna cannot be Primordial, 

 but he considers that it is intermediate between this latter and the 

 Llandeilo fauna. There is a very significant similarity between 

 many of the Lamellibranch genei'a of the 'gres armoricain' and 

 those occurring in the Trenton and Chazy groups of Canada and the 

 United States, thus indicating a nearer relation to these rocks than 

 to the underlying Calciferous formation in these countries. Again, 

 when compared with British strata, the molluscan fauna of the 

 * gres armoricain,' approaches nearer to that of the base of the Arenig 

 than to that of the older Tremadoc. If this supposition is correct, 

 the fauna of the ' gres armoricain ' cannot correspond with the 

 earliest period of the second Silurian fauna, and consequently 

 neither a Tremadoc nor a Primordial fauna has yet been discovered 

 in Brittany. Notwithstanding the identity of the Bilobites and 

 Scolites in the ' gres armoricain ' with those of the Lingula Flags, 

 the author states that these rocks cannot be compared together in 

 point of age. 



Touching the classification of the schists, conglomerates, phyllades, 

 etc., which in Brittany occur beneath the ' gres armoricain,' con- 

 siderable differences of opinion exist among French geologists, but 

 Dr. Barrois adopts that of Diifrenoy, and considers the Etage of 

 Gourin to correspond with the horizon of the Primordial fauna, and 

 the phyllades of St. L6 with the Longmyndian of Callaway. 



G. J. R 



