14 BIOLOGICAL SOCIETY OF WASHINGTON. 



of such a sea, and the land fauna and flora which existed upon 

 its borders. I have upon several occasions called attention to the 

 fact that brackish and fresh-water faunas have undergone far less 

 differentiation during the lapse of geological epochs than marine 

 faunas have. I cannot now contrast the aqueous fauna of the 

 Laramie Group with any open-sea fauna, but, together with its 

 contemporaneous flora and land molluscan fauna, it contrasts 

 strangely with its contemporaneous land vertebrate fauna. 



The aqueous fauna of the Laramie Group is mainly molluscan ; 

 and while the brackish- water forms show their relationship to the 

 preceding Cretaceous marine fauna, the fresh- water and land 

 mollusca are largely of types that now exist. The flora is also 

 of a very modern character ; but the vertebrate land fauna is 

 largely Dinosaurian. I need not tell a paleontologist that here 

 is a most remarkable mixture of types. The extraordinary bio 

 logical character of this group will be still more conspicuously 

 seen when I mention that I have collected the characteristic 

 mollusca of this group where they were associated with Dino 

 saurian remains ; and in the same series of layers I have also 

 obtained numerous species of plants, several of which have by 

 competent authority been identified with European Miocene 

 species, and two of them with species now living in the United 

 States. That is, we have evidence that a large molluscan fauna, 

 and a luxuriant dicotyledonous flora, both containing species that 

 we can with difficulty, if at all, distinguish from living forms, 

 existed contemporaneously with great Dinosaurian reptiles such 

 as have always been regarded as peculiar to the Mesozoic age. 



The instances which I have presented demonstrate that in 

 different parts of the world there are many and material depart 

 ures from the European paleontological standard ; but in no case 

 have we seen that departure to be so great when marine forma 

 tions are compared with each other as they are when formations 

 containing a marine fauna are compared with those containing 

 a continental fauna or flora. I therefore quite agree with those 



