SUMMARY. 117 



Alps, and thence they passed southerly into the Italian basin. Migrants also 

 passed in all other directions into the residual basins to the north and south 

 of the basins of the C6te d'Or and South Germany, in the province of Central 

 Europe. 



While these faunas in the Northeastern Alps and Italy became analdainic 

 faunas so far as the Arietidaa were concerned, they were aldainic faunas for some 

 other groups, like the Lytoceratidse, and also very likely for the Liparoceratidas, 

 Deroceratidae, and possibly other families. These mixed faunas, which have been 

 deemed such sources of confusion, are in reality the most instructive, and will 

 enable us to trace both chronological and chorological migrations with greater 

 security, if the views here advanced are correct. 



Table V. shows that there are but two examples of what Neumayr calls cryp- 

 togenous types in Central Europe, species appearing suddenly without apparent 

 ancestors, Schlot. catenate/, and Psil. planorbe, var. leve. Schlot. catenata, however, 

 cannot be called an unquestionable cryptogenous form in the Northeastern Alps. 

 It is in that basin connected by intermediate forms, as stated above, with Psilo- 

 ceras, and it is therefore probable that in course of time the geological evidences 

 which are now confusing will be brought into accord with the paleozoblogy. 

 Psil. planorbe is a radical derived from Psil. caliphjllum, or else from pre-existing 

 triassic ancestors, and the absence of a complete series connecting it or Psil. 

 caliphjjllum with Gymnites of the Trias is evidently due to the absence of an 

 equally complete series of formations. That the intermediate species might have 

 been deep-sea forms, and therefore not represented in the rocky strata now 

 exposed, as supposed by Neumayr, is an admissible explanation. Newberry's 

 hypothesis 1 of the retirement of the sea is, however, equally supposable, and has 

 the additional recommendation of explaining the absence both of intermediate 

 forms and of the sediments. Newberry thinks that the presence of intermediate 

 links in paleozoologic history, and their absence from localities so far explored, 

 are explicable on the supposition that the chain of the rocky deposits is incom- 

 plete in those localities, and that the sea had retired from them carrying with it 

 the threads of life. The missing links of the record were then evolved in other 

 places, but not brought back by the return of the ocean to its former shores. 

 This seems to us more in accord with what is already known of the merely frag- 

 mentary aspect of the geologic record in any one region, the occasional discov- 

 ery of the absent leaves of the record in other places, and the want of absolute 

 synchronism between the strata of Europe and those of America. 



That Psil. planorbe was a littoral form, as well as its congeners, can hardly be 

 doubtful, since, besides the facts quoted above, they are found associated in the 

 same series of layers with bones of saurians and even remains of insects in Eng- 

 land. The remarks of Martin and other authors, quoted above, upon the charac- 

 teristics of the lumachelle in the C6te d'Or, and the broken aspect of the shells 

 of Ammonoids compared with those of swimmers like the Nautiloids, as stated 

 by Terquem, in the department of Moselle, the opinions of Tate and Blake, and 



1 Circles of Deposition in American Sedementary Rocks, Proc. Am. Ass. Adv. Sci., XXII., 1873, 

 pp. 185, 189. 



