34 MUSEUM OF COMPARATIVE ZOOLOGY. [Jan. 



zoological affinities, there has been no effort to do more than 

 follow the most acceptable of the existing systems. 



In the stratigraphical division, grouping has in the main only 

 been carried so far as to bring together those forms belonging 

 to each great group of formations, making only ten divisions of 

 the whole geological section. This incomplete separation has 

 been rendered necessary by the difficulty of determining the 

 precise synchronism of fossils from widely separated points. In 

 dividing the specimens so as to correspond to the distribution 

 in space or faunal arrangement, a different plan has been fol- 

 lowed from that adopted in the two divisions above referred to ; 

 while with them only general results were aimed at, in this 

 division it has been deemed best to carry the separation as far 

 as possible. Constant effort is made to keep all the specimens 

 of each species from any locality together, so that the important 

 questions connected with the distribution of forms may be 

 determinable from the specimens. Where fossil fauna? have 

 been recognized, the different localities have been grouped 

 under that head ; where the ancient limitations were not readily 

 determinable, the most convenient geographical divisions have 

 been adopted. 



Lists are being prepared which will show in their alphabeti- 

 cal order the names of the localities on each continent from 

 which we have specimens. In preparing these lists the localities 

 of each set of formations such as the Tertiaries or Cretaceous 

 series constitute separate lists. Where known, the precise posi- 

 tion of the beds at the locality is given, also the name of the 

 collector, or if many, that of the best known and most accurate 

 of them, as authority for the occurrence of certain beds at 

 such a point. Where the locality is not well known the lati- 

 tude and longitude of the point will, if possible, be given. 



In the class of Gasteropoda, the lists above referred to are 

 nearly complete. It will give some idea of the magnitude of 

 our collections that from the tertiary beds of Europe alone we 

 have over five hundred localities represented in this class. 



It is a part of the plan to have for each class of which large 

 numbers of forms are found fossil, a series of maps represent- 

 ing the development of the great formations on all of the Con- 

 tinental masses, each map having affixed to it numbers corres- 

 ponding to the numbers placed against the localities in the 



