88 



classes themselves, it is surely more necessary to be careful in 

 our classification of the isolated beds of a system into sub- 

 divisions, when we take into consideration the horizontal dis- 

 tribution of organisms as affected by migration of colonies, 

 physicial barriers and local influences. 



As an example of classification which might ignore the 

 effect of migration of species, it is interesting to notice that 

 although the shell Pectunculus laticostatus (Lamarck)* so abun- 

 dant in the lower shell bed at Table Cape, is not now found 

 living near the shores of Australia or Tasmania, it still exists 

 in abundance on the coast of the distant colony of New Zea- 

 land. It is possible that this shell had a wider distribution 

 during the tertiary period ; but if there be evidence to the 

 contrary, it is probable that change of circumstances have 

 caused the species to migrate from its original centre, and 

 that the great distance of our coast from the shores of New 

 Zealand, represent horizontally or in space, the long 

 duration of time necessary for the slow migratory progress 

 of such an organism. 



Take again the following instance : — 



In the Turritellaf liaiestone of Flinders Island, there 

 o'ccurs three species of shells also common to Table Cape 

 deposit ; one of them being the shell so abundant at the latter 

 place. Cucullea caiiiozoica (Tenison-Woods.) Had an observer 

 only reported the discovery of these three forms, without 

 reference to their abundance or associated organisms, it would 

 be a reasonable enough inference, so far as evidence went, 

 that they belonged to the same sub-division. But as I have 

 fuller evidence which informs me that, with the exception of 

 the organisms already referred to, the characteristic shells of 

 Flinders Island, though there very numerous, had never been 

 detected in the beds of Table Cape. This knowledge, taken 

 in conjunction with the consideration that the latter beds 

 have now been very fully investigated, is sufficient to postpone 

 the final co-relation of these deposits until the other isolated 

 formations, of a similar character, afford some additional clue 

 to their exact position. 



As an example of local distribution in the same bed at 

 Table Cape, I noticed, especially that CuliQ,hna arachis (Quoy) 

 though very common at one particular point, could be found 

 nowhere else in the same horizon or indeed anywhere else. 

 This is another important consideration when comparisons 



* At Table Cape this shell has invariably 29 radial ribs, not 39 as figured 

 and described by Prof. McCoy in the Victorian Decades. 



t A very different species tu that which characterises the Turritella group 

 at Table Cape. 



