1870.] 



Presents. 



335 



plants were more varied, and the facilities for migration of species less ex- 

 tensive, than in the Carboniferous. 



In comparing the Erian flora of America with the Devonian of Europe, 

 we meet with the difficulty that little is known of the plants of the Lower 

 and Middle Devonian in Europe. There are, however, specimens in the 

 Museum of the Geological Survey which show, in connexion with facts 

 which can be gleaned from the works of continental writers, that Psilo- 

 phyton occupied the same important place in Europe which it did in Ame- 

 rica ; and in the Upper Devonian the generic forms are very similar, though 

 the species are, for the most part, different. 



In Eastern America no laud flora is known below the Upper Silurian ; 

 and even in that series the plants found are confined to the genus Psilo- 

 phyton. Independently, however, of the somewhat doubtful Lower- Silu- 

 rian plants stated to have been found in Europe, there are indications, in 

 the Lower-Erian flora, that it must have been the successor of a Silurian 

 flora as yet almost unknown to us ; and the line of separation between this 

 old flora and that of the Devonian proper seems to be at the base of the 

 Middle Devonian. 



In applying these facts and considerations to the questions relating to the 

 introduction and extinction of species, and the actual relations of successive 

 floras, it was proposed to compare what might be called specific types, — that 

 is, forms which in any given period could not be rationally supposed to be 

 genetically related. Of such specific types, at least fifty may be reckoned 

 in the Erian flora ; of these, only three or four are represented in the Car- 

 boniferous by identical species, while about one half are represented by 

 allied species. The remainder have no representatives. 



A Table of specific types of the Erian was given, and its bearing shown 

 on the questions above referred to ; and the hope was expressed that by 

 separating such types from doubtful species and varietal forms, some pro- 

 gress might be made towards understanding, at least, the times and con- 

 ditions in which specific types were introduced and perished, and the range 

 of varietal forms through which they passed. 



Presents received April 7, 1870. 



Transactions. 



Berwickshire Naturalists' Club. Proceedings. Vol. V. No. 3. 8vo. Aln- 

 wick 1865. The Club. 



Lyons : — Academie Imperiale des Sciences, Belles-Lettres et Arts. Me- 

 moires. Classe des Sciences. Tome XVII. 8vo. Paris 1869-70. 



The Academy. 



Naples : — Societa Eeale. Kendiconto delle tornate c dei lavori dell' 

 Accademia di Scienze Morali e Politiche. Anno 8. Settembre-Di - 

 cembre 1869. 8vo. Napoli 1869. The Academy. 



