NATURAL SCIENCES OF PHILADELPHIA. 



13 



Colorado at the last meeting of the Academy, although LeConte 

 and others had regarded them as probably miocene.' lie stated, 

 moreover, that the evidence from palaeontology was discrepant, 

 and that it must be conceded that a tertiary flora was contempo- 

 rary with a cretaceous fauna. lie quoted Dr. Hayden as having 

 shown that there was no phj'^sical interruption in the series of 

 deposits above enumerated, and that the incongruity in the palae- 

 ontology is to be regarded as e-vidence that no extinction or re- 

 creation of a general character had taken place during this time; 

 that the apparent interruption in the vertebrate life in the dis- 

 appearance of large land saurians and appearance of land mam- 

 malia is due to the irruption of the latter by migration probably 

 from the south. 



February 3. 

 The President, Dr. Ruschenberger, in the chair. 

 Eighteen members present. 



Dr. Chapman exhibited a dissection of 

 one of the hind legs of a muskrat, Fiber 

 zibethicus. The tendons of the tibialis 

 anticus (a), extensor proprius hallucis (6), 

 and extensor longus digitorum (c), pass 

 down a groove in the tibia and under a 

 little process of bone {d). The extensor 

 longus digitorum is held down by an 

 additional process {e). This arrangement 

 seems to quicken the extension of the foot, 

 and is of use apparently to the animal in 

 swimming. 



Remarks on Protozoa. Prof. Leidy re- 

 marked that while it was exceptional to 

 find the same species of the higher sub- 

 kingdoms in the difierent parts of the 

 world, it appeared to be the rule that 

 most species of Protozoa were found everywhere under the same 

 conditions. A large number of our fresh-water forms he had 

 recognized as the same as those described by European authors. 

 A less number of species are pi'obably peculiar to every region. 

 Among our fresh-water Ehizopods he had observed not only the 

 genera Ainceba, Arcella, Diffiugia, Euglypha, Trinema, Lagynis, 

 ActinophrySy etc., but also most of the species of these as indi- 

 cated by European naturalists. 



1 LeConte, Notes on Geol, Pacific R. R. Co., 1868, p. 65. 



