NOTES AND EXPLANATIONS. 



(MIOCENE LIST.) 



1 and 2 — Are not true Astrasas. 



3 = Columnaria? sexradiata, Loxdsale, Quart. Joum. QeoL Soc. VI, 



1845, 497. 

 6 = Lithodendron lineata, Cokkad, Trans. Geol. Soc, Pa. 1,1835,340, 



xiii, 4. 



43 = Orbicula lugubris, Conkad, Mioc. Foss. 75, 43, 2. 



44 = Orbicula multilineata, Conkad, ib. fig. 3. 



45 =Terebratula nitens, Coxkad, U. S. Espl. Exp. X, 726, 19, la, I 



see Mr. Carpenter, in his valuable report to the British Asso- 

 ciation on the Moll. "West Coast N. A. (1863, 680), expresses the 

 opinion that this is very probably identical with the recent 

 Waldheimia pulvinata, Gould.' On examining the typical spe- 



' The extensive and critical knowledge of the living Mollusks of the 

 Western Coast of North America, possessed by this able conchologist, ren- 

 ders his remarks on the relations of Tertiary and existing species of that 

 region unusually interesting to the palaeontologist. It is to be regretted? 

 however, that his comparisons were, in most cases, necessarily made with 

 very imperfect figures of the fossil species ; the type specimens not being ac- 

 cessible at the time he was in this country. Hence, his suggestions that so 

 large a proportion of the Miocene shells of the Pacific slope are, probably, 

 identical with living species should not be too hastily accepted. Particularly 

 since the questions involved are of far greater importance than that of the 

 mere-specific difference or identity of certain forms, for if wrongly decided, 

 they may lead to very erroneous conclusions in regard to the age of tbese 

 tertiary deposits ; while they have a direct and important bearing on the 

 discussions respecting the duration of specific types in time. Consequently, 

 I have carefully compared the types of Mr. Conrad's Western Coast Terti- 

 ary species, witli their living representatives, in all cases where authentic 

 examples of eacli were at hand, and give the results ot these comparisons 

 under each of the species in these notes. 



In most of these cases, it will be observed, I have arrived at the con- 

 clusion that the fossil shells are distinct species from the recent. This 

 accords with the conclusions, in many cases, adopted by those who 

 have of late years, instituted careful comparison of the Miocene species 

 furmeriy supposed to be identical with living forms. 



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