22G GEOLOGICAL DISTRIBUTION. 



mon to the Cretaceous area comprised within the States of Alabama 

 and Mississippi (forty-eight species to Alabama, twenty-seven to 

 Mississippi), lying some four hundred miles farther to the south, 

 and thus separated by an interval considerably exceeding that which 

 separates the Mediterranean and Baltic zones of the continent of 

 Europe. On the other hand, of about two hundred species cata- 

 logued as belonging to the State of Texas only some ten or twelve 

 are indicated as forming a part of the Mississippi and Alabama 

 faunas, although the last occupied a position but little removed, 

 either geographically or climatically, from the Texan. These facts 

 are hardly in consonance wnth the conclusions which have been 

 reached respecting the past distribution of climatic zones, and, if 

 broad diifei'ences do obtain between certain contiguous north and 

 south faunas, as is undoubtedly the case, their explanation must be 

 sought in causes other than those directly connected with clima- 

 tology. The nature of the sea-bottom, depth of water, &c., may 

 have had much to do in the matter. 



Despite what may appear as overwhelming evidence, proving 

 exceptionally broad distribution in the past periods of the earth's 

 history, even as late as the Jurassic and Cretaceous periods, Professor 

 Neumayr *" and others have attempted to show that this condition 

 did not actually exist, at least as far as the Mesozoic era is concerned, 

 and that in reality specific cosmopolitanism is as well-pronounced at 

 the present time as it was formerly. Thus, it is contended that the 

 modern pelagic Mollusca, more particularly the Pteropoda, are of 

 exceedingly wide distribution, and that even among the Cephalo- 

 poda a considerable number of more or less cosmopolitan forms — 

 among them Argonauta Argo and A. hians — are to be met with. 

 Furthermore, it is urged that, if well-marked faunal variations are 

 manifested along the oceanic border, such variations do not obtain in 

 the oceanic abyss, where a uniform type dominates the faunal facies, 

 and with whose fauna many of the ancient life-series are to be com- 

 pared. The facts relating to the distribution of the Mollusca, mod- 

 ern and ancient, that have already been given, are sufficient to prove 

 the general erroneousness of the proposition here stated, and, if any 

 more proof in this direction were needed, none more significant 

 could be had than that drawn from the distribution of a member of 

 one of the very groups of animals cited by Neumayr, the Cephalo- 

 poda. The nautilus, which to-day appears to be restricted to the 



