THE SUCCESSION OF ANIMAL FORMS l8l 



precisely as at present ; while in many places, as on the Lower 

 St. Lawrence, we find them living together on the same banks, 

 and yet preserving their distinctness. 1 Nor are there any in- 

 dications of a transition between the two species. I might 

 make similar statements with regard to the Astartes, Bucci- 

 nums and Tellinae of the drift, and could illustrate them by 

 extensive series of specimens from my own collections. 



Another curious illustration is that presented by the Tertiary 

 and modern faunae of some oceanic islands far separated from 

 the continents. In Madeira and Porto Santo, for example, 

 according to Lyell, we have fifty-six species of land shells in 

 the former, and forty-two in the latter, only twelve being com- 

 mon to the two, though these islands are only thirty miles 

 apart. Now in the Pliocene strata of Madeira and Porto 

 Santo we find thirty-six species in the former, and thirty-five in 

 the latter, of which only eight per cent, are extinct, and yet 

 only eight are common to the two islands. Further, there 

 seem to be no transitional forms connecting the species, and 

 of some of them the same varieties existed in the Pliocene as 

 now. The main difference in time is the extinction of some 

 species and the introduction of others without known connect- 

 ing links, and the fact that some species, plentiful in the 

 Pliocene, are rare now, and vice versa. All these shells differ 

 from those of modern Europe, but some of them are allied to 

 Miocene species of that continent. Here we have a case of 

 continued existence of the same forms, and in circumstances 

 which, the more we think of them, the more do they defy all 

 our existing theories as to specific origins. 



Perhaps some of the most remarkable facts in connection 

 with the permanence of varietal forms of species are those 

 furnished by that magnificent flora which burst in all its 

 majesty on the American continent in the Cretaceous period, 

 and still survives among us, even in some of its specific types. 

 1 Paper in Record of Science, on Shells at Little Metis. 



