32 MUSEUM OF COMPARATIVE ZOOLOGY. [Apr. 



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zoological arrangement of the fossils has been pushed in many 

 sections of the work to genera and species. 



I should add that I have been efficiently assisted, in a portion 

 of the general work of preliminary arrangement, particularly 

 of the fossils of the later Palaeozoic times, by Mr. St. John, who 

 is to devote himself especially to the identification and arrange- 

 ment of these fossils, with a view to the more exact determina- 

 tion of the several horizons to which they belong, and of other 

 kindred points. 



In carrying out the plan which has already been noticed at 

 some length, I have perhaps taken more than usual pains to 

 make a complete separation of the Tertiary fossils from all the 

 others in the Museum. Having previously brought together 

 nearly all the Tertiary Gasteropods, I have recently made an 

 especial effort that no Corals nor Acephala might be left out ; 

 consequently, I have now nearly all the Tertiary invertebrata, 

 not only brought together, but, for the most part, arranged 

 zoologically, not merely according to orders, but according to 

 genera and species as well. From indications furnished by the 

 investigations thus far made on these fossil forms, it seems 

 probable that the Tertiary formations will naturally fall into 

 five general periods, consisting, on an average, of two or three 

 well marked subdivisions or horizons. 



While various groups of the Lamellibranchiates of the Ter- 

 tiary have been worked up to about the same point, the oysters 

 on the whole, are the most advanced. They have been exam- 

 ined with great care ; there has been a thorough verification of 

 the names of all such as have labels ; those remaining, without 

 accompanying names, have been for the most part identified, so 

 far as the means have been at my disposal ; so that the Tertiary 

 oysters, as a group, promise to be soon ready for the exhibition 

 room. In this part of my work I have found constant occasion 

 for Miss Sarah Cutler's intelligent and careful handiwork. 



With a view to supplying deficiencies, but especially to inves- 

 tigating more thoroughly and intelligently, not only the Muse- 

 um collection of Tertiary Shells, but of the American Terti- 

 aries generally, extensive explorations of the Tertiary strata of 

 the southern Atlantic and Gulf States were made last summer. 

 Tertiary Fossils were gathered at various points, and occasion- 

 ally some belonging to the Cretaceous and other ages. As soon 



