Ch. XV.] MIOCENE AND LIVING PLANTS. 267 



On the leaves of a fossil maple, Acer trilobatum, already mentioned, 

 fig. 183, p. 253, a small body is frequently seen resembling, the living 

 fungus which grows on maples, called by Fries Bhytisma acerinum. 

 It is tuberculated and crenulated (see the magnified figure, b). The 

 fossil has made so deep an indentation on the incumbent and subja- 

 cent layer of marl as to lead Professor Heer to infer that it was some- 

 what thicker than the living form. Instead, therefore, of treating it 

 as a variety, he has called it R. induratum, under which title it helps 

 to swell the list of extinct Miocene species. 



In like manner there is a minute fungus, called by Heer Sphoeria 

 ceuthocarpoides, which spots the leaves of Populus ovalis at (Eningen, 

 very closely resembling the living Sphoeria ceutJiocarpa of Fries. Some 

 botanists would think it very hazardous to assign even generic names 

 to such objects, and still more rash to decide that the fossil differed 

 specifically from its living analogue. 



Another of these fungi forming black spots on the fossil leaves of a 

 poplar is proved in like manner to have been a real subtance, and not 

 simply the effect of discoloration, for it has left indentations both on the 

 under and overlying layers of marl. To decide that it is not a living- 

 species would require far ampler data. Some botanists are even un- 

 certain whether as much can be said of the Populus latior itself of 

 (Eningen, on which the fungus grew, and of which seven varieties are 

 described by Heer, some of them coming very near to the Populus 

 mmilifera of North America. 



Similar comments might be made on the long list of homologous 

 insects given by Heer from the Miocene strata of Switzerland. 

 Their specific distinctness from their nearest representatives now liv- 

 ing might appear to the zoologist in a very different light, according 

 to the state of mind in which he may approach their study. If he is 

 reflecting on the fact that all the Upper Miocene mammalia and a 

 great majority of the testacea are extinct, and is then endeavoring to 

 decide whether a fossil and a recent form, between which there is a 

 close affinity, should be regarded as varieties or distinct species, it 

 may seem the safest course to incline to the latter alternative ; yet, by 

 giving a new name to the fossil in doubtful cases, a serious responsi- 

 bility is incurred, as the naturalist thereby commits himself to an ab- 

 solute negation of specific identity between such Miocene and living 

 insects and plants. If it be right to exercise extreme caution in iden- 

 tifying, it is equally important not to separate individuals which may 

 really belong to the same species. In spite of the soundness and 

 general accuracy of the conclusions arrived at by Professor Heer after 

 such great and conscientious labors, there appears to me an inconsis- 

 tency in one of his results, which may have been owing to an unwill- 

 ingness to identify Upper Miocene and living plants. "When we 

 consult his tabular list of the fossil plants of Switzerland, we find that 

 a great number of species pass from the Aquitanian Flora to that of 

 (Eningen, which are as distinct from each other in age as are the Fon- 



