The Invertebrate Fauna of the Uitenhage Series. 59 



many apparently cosmopolitan forms, some of the most characteristic 

 and highly specialised types follow a very different distribution. It 

 might perhaps be supposed that members of this class, owing to 

 their relatively passive habit, were more inured to varied environ- 

 ment than the cephalopods, while these, on the other hand, possibly 

 equipped with better facilities for exercising choice of station, were 

 more delicately adjusted to conditions of temperature, ood-supply, 

 and other special characters of environment. Nothing, however, is 

 known regarding the exact mode of life of these cephalopod-types ; 

 but while the evidence so ably handled by Neumayr seemed for 

 some time inevitably to urge the acceptance of his fascinating theory, 

 a body of facts has since been brought to knowledge which must 

 surely indicate that climatic conditions played at the most an insig- 

 nificant part in regulating the dispersion of ammonites, and that 

 distribution of land and sea is in reality to be recognised as the most 

 potent determining factor.* It is therefore scarcely conceivable that 

 in the case of the Uitenhage fauna a distribution of land and sea 

 which permitted the migration of well-characterised lamellibranch- 

 forms over such a wide area, could have offered any obstacles to a 

 similar geographical range for some, at least, of the cephalopod types. 

 It must be remembered, too, that members of the true Holco- 

 stephanus (Pavlow's Asticria) have been described from the Mazapil 

 district in Mexico.! 



It becomes plainly apparent that with the limited evidence as yet 

 available, the only reasonable course is to suspend judgment con- 

 cerning the exact significance of the Uitenhage Cephalopoda in this 

 question of distribution, and a definite pronouncement will only be 

 justifiable when our knowledge of the Indian and African Neocomian 

 faunas is more complete. In view of the facts to which reference 

 has already been made, it is necessary to abandon the supposition 

 that these cephalopods were excluded from the equatorial waters ; 

 but in the meantime there is nothing to show whether the absence 

 of these forms from the Neocomian of German East Africa and 

 Cutch is merely apparent, in which case the fact of their occur- 

 ence there may become established by extended search, or whether 

 it is real, and to be accounted for by causes of a local character. In 

 this connection it is well to bear in mind that in Europe certain 

 Cephalopoda of the Chalk, though living under conditions which 

 might be expected to have assured exceptional uniformity of environ - 



* Kossmat (2), p. 53; Nikitin (2); Burckhardt (2), pp. 115-135; Solger (1), 

 pp. 220-221 ; G. Boehni (2) ; Tornquist (1), p. 285 ; Ortmann (1) ; Stanton (2) 

 Burckhardt (3), p. 179. t Burckhardt (3), p. 183-185. 



