276 Notices of Memoirs— De 8aporf.a — Jurassic Plants. 



Considered as a whole, the Jurassic vegetation seems to have been 

 poor, monotonous, and almost entirely composed of tough plants 

 with hard and meagre foliage, little capable of furnishing nourish- 

 ment to animals. Thus the contemporary terrestrial animals 

 were generally carnivorous, and the mammifers particularly nearly 

 all insectivorous. The small dimensions of most of the plants 

 of this epoch result from the comparison of their different organs 

 with those of species which correspond to them in the same 

 natural Order. The largest Jurassic Cycadacece are not equal to 

 those of our time ; several were far smaller, or even were only a few 

 inches high. So also with a great number of Ferns. We do not 

 find in the plants the gigantic proportions assumed by the greater 

 number of the contemporary reptiles. However, to avoid exaggera- 

 tion, we must state that the fronds of some ferns must have measured 

 a considerable size in their integrity, and that the Coniferce, especially 

 the Ciipressinites, present arborescent types of the first magnitude. 

 Nevertheless, when one studies the Jurassic plants closely, nothing 

 rich or luxuriant discloses itself, and one is struck by the ex- 

 treme simplicity of the group. Equisetacece, Ferns, Gijcadacem, 

 Coniferce, some rare Monocotyledons, are the sole constituent elements 

 of the terrestrial vegetation. Add some rather rare Characece and 

 AlgcB, and we shall have enumerated all the Orders of plants which 

 peopled the land and waters of our country at that period. These 

 are some of the most startling peculiarities that the study of these 

 diverse groups brings to light. 



The list oi AlgcB\% in accordance with the importance of the marine 

 deposits and the predominance of the seas, at an epoch when central 

 Europe still formed an archipelago, whose islands tended to unite 

 themselves without being definitely welded into a single continent. 

 To explain the method of determination which I have applied to the 

 Jurassic Algce would carry this beyond the bounds of a simple notice. 

 It is very evident that the greater number of these jDlants must 

 have perished without leaving any trace. The impressions which 

 have come down to us are all the more interesting, and — irrespective 

 of doubtful forms which the desire of being complete urges an 

 author to desci'ibe, without having a very lively faith in the objects 

 which he desires conscientiously to make known — there exist others 

 that are trustworthy ; an examination of these suggests many curious 

 remarks. Thus the class of Algce, conformably with what has taken 

 place in the greater number of marine organisms, has altered very 

 gradually, and the obstinate persistence, so to speak, of certain types 

 of Jurassic Algce, establishes this in a sm-prising manner. In sup- 

 port of this I will adduce three kinds of Algca chosen from those best 

 characterized : to two of them I have given the names Siplionites 

 and Cancelloplycus; the third is the large genus Chondrites, Sternb., 

 several times altered, but very natural when we only include species 

 with the same facies. The connexion between Chondrites and the 

 existing Gigartince is the more probable, as several of the Jurassic 

 species exhibit globular swellings, very analogous to the Sporangia 

 of the living members of this family. The Chondrites were without 



