66 Cincinnati Society of Natural History. 



the limits of a family when the living genera and species 

 present so many variations in their forms and aspects, even 

 when one is familiar with the more important characters 

 establishing the exact similarity, such as the internal organi- 

 zation and the mode of fructification, characters that we can 

 never observe in the fossils. In these, one is confined to 

 external characters, that show the appearance, the form and 

 the general aspect of the plant after it has passed into a fossil 

 state. We believe, however, that all the world is in accord 

 with us in placing in the family of non-articulate Algse the 

 species that we have placed with certainty in this family. 

 Among those we have put with doubt at the end of the genus 

 Fucoidcs, there are only two that I have seen for myself, and 

 their form is so singular that we have not placed them with 

 certainty among the marine plants ; we do not know the 

 four others, except from the figures of M. Schlotheim, and we 

 have already said of these figures that they differ so widely 

 from all the Algae described and figured by botanists, that we 

 doubt much their forming part of this family. 



While there seems to us little doubt as to the position the 

 fossils that we describe in this memoir should occupy in the 

 vegetable kingdom, it is not the same with the distinction of 

 species ; in reality, nothing can be more embarrassing than to 

 tell which of these fossil bodies, generally verj- variable in 

 the same species, should be considered as species and which as 

 varieties. It becomes much more difficult when one must 

 often decide for himself from few specimens; we believe, there- 

 fore, that when a great number has been observed, we may, 

 perhaps, be obliged to unite many species in one. But for 

 the present it has appeared more convenient to separate all 

 that offer such distinct characters as to lead to the presump- 

 tion that the fossils belong to dififerent species. 



In regard to the horizon of these vegetable fossils, it should 

 be remarked that all those known at present belong to four 

 dififerent formations: i. The Fucoides of Monte-Bolca, near 

 Verona. I shall say nothing of this celebrated locality, my 

 father having described it with details in the memoir he has 

 published on the calcareous traps of Vicentin. I repeat only 

 his statement, that this terrane is a sedimentary formation 

 above the Tertiary, and I would remark that the fossil ])lants 



