io6 THE POPULAR SCIEXCE MONTHLY. 



In 1874 he predicted that the ancestor of all the mammals would 

 be a five-toed, fiat-footed walker, with tubecular molar teeth, or in ex- 

 act language, a pontadactyl, plantigrade bunodont. Seven years after, 

 he obtained evidences that such a type of mammals abounded in North 

 America during the early Eocene Tertiary period. Professor Cope,* 

 in his phylogeny of the camels, shows a remarkable parallel to that of 

 the horse, both forms appearing in the Lower Eocene. Mr. Eugene N. 

 S. Ringuebergf belicA'es he has found in a thin layer of limestone at 

 Gasport, New York, a deposit in which a number of forms of brachio- 

 pods seem to present the intermediate stages between certain brachio- 

 pods common to the Clinton and the group of rocks immediately above. 

 While the majority of species in this deposit belong to the Niagara, 

 there are among the fossils met with three species of brachiopods which 

 were supposed to have passed out of existence with the Clinton. He 

 finds in this bed thirty-two forms peculiar to the Niagara, eleven com- 

 mon to Niagara and Clinton, three belonging to the Clinton, and two 

 characteristic forms of the transition grouji. Many of these show in- 

 termediate characters. 



Professor II. S. Williams,J in his paleontological studies of the life- 

 history of Spirifcr Icevis, in which he traces the ancestral line of this 

 creatui-e, says : " Whatever theoretical description we may give to 

 species, here are, in the first place, an abundance of individual organ- 

 isms whose remains are found in the Upper Silurian rocks of Europe, 

 Great Britain, and America, presenting a few clearly marked, distinctive 

 characters, which are found variously developed in the individual forms, 

 but so grading in the various varieties as to cause careful naturalists 

 to associate them as varieties of a single species." 



Dr. C. A. White,* in his comparisons of the fresh-water mussels 

 and associated mollusks of the Mesozoic and Cenozoic periods with 

 living species, expresses his belief that the present Unios of North 

 America, particularly those forms allied to Uiiio davits, have come 

 down in an unbroken line from the Jurassic and possibly from earlier 

 times. He shows that thus far all the fossil ZJhios have been obtained 

 from lacustrine deposits, none of these beds being distinctly fluvia- 

 tile. He furthermore calls attention to the fact that " these lacustrine 

 formations are of very great extent in Western North America, and, 

 without doubt, the lakes in which they were deposited were caused by 

 encircling bands of rising land during the elevation of the continent. 

 These great landlocked waters were at first brackish, but finally be- 

 came, and for a long time remained, fresh, continuing so until their 

 final desiccation." From this commingling of salt and fresh water he 

 justly assumes that many modifications arose in the forms of Unios 



* " American Naturalist," vol. xx, p. Gil. f Ibid., vol. xvi, p. "711. 



X " American Journal of Science and Arts," vol. xx, p. 456. 



*" Bulletin of the United States Geological Survey of the Territories," vol. iii. 

 No. 3. 



