424 O. Meyer — Genealogy and Age of the Species 



lived in Alabama, and among their remains maj r be a fossils. 

 Since, therefore, we do not know a fossils, and since /3 fossils 

 are useless, there remain only y and d fossils for the determina- 

 tion of a bed. A single d fossil counts for little, but a number 

 of them affords cumulative evidence. Of the greatest import- 

 ance for our purpose are the y fossils, since a great number be- 

 long in this class, while 3 fossils are comparatively scarce. If 

 we find, for instance, in a new bed nothing but Astarte sulcata 

 Lea, Venericardia rotunda Lea and Mitra pactiiis Conr., and all 

 these in that form in which they occur in the typical Claiborn- 

 ian bed, we may be justified in referring such a bed to the 

 Claibornian. For such a comparison, however, it is essential 

 that we recognize and state the differences in the forms as they 

 occur in the three beds. If a difference between two y forms is 

 not recognized, this y fossil becomes useless for the identifi- 

 cation of beds. For instance, if Mr. Aldrich sees no difference 

 between Venericardia rotunda Lea and Yen. diver sicleniata Meyer, 

 but says they are alike (his article, p. 307), it is of no use, that 

 he cites Yen. rotunda among those forms, which demonstrate 

 the Claibornian age of a bed (p. 306). If we observe the dif- 

 ferences, however, these y fossils (we may speak here of "recog- 

 nized " y fossils) are as valuable as d fossils are. 



As the result of these examinations, we can say now the fol- 

 lowing: 



1. There are no a fossils. That is, there exists no single spe- 

 cies from which alone we can characterize with certainty a bed as 

 Claibornian, etc. 



2- y fossils which are not "recognized," and /3 fossils are useless 

 in the determination of beds. 



3. Beds can be determined only by 8 fossils and "recognized " 

 y fossils. 



Having now collected in Vicksburg, Jackson and Claiborne 

 many species which were not known before, or known only from 

 one of the localities at the time of Hilgard's observations, I have 

 seen, that a number of such species which he, according to our 

 classification, had to consider as 8 fossils do not belong to this 

 class and that others exist, which he did not know. Moreover, 

 and this is more important, he did not use in a systematic way 

 the method of " recognizing" the y fossils. After having worked 

 according to the above method, and with my present knowledge 

 of the fossils, through all his determinations of beds, I come to 

 the conclusion, that some of them are imaginary, many of them 

 may be probable, but no one is fully established. As a positive 

 determination of the beds, however, is the foundation of conclu- 

 sions I made my statement A: "only a competent and careful ex- 

 amination of the fossils could indicate the relations of the Old-ter- 

 tiary strata of Mississippi." 



