1865.] CARPENTER — STRUCTURE OF EOZOON. 119 



2. The difficulty arising from the zoophytic plan of growth of 

 Eozoon is at once disposed of by the fact that we have in the 

 recent Polytrema (as I have shown, op. cit. p. 235) an organism 

 nearly allied in all essential points of structure to Rotalia, yet no 

 less aberrant in its plan of growth, having been ranked by Lamarck 

 among the Millepores. And it appears to me that Eozoon takes its 

 place quite as naturally in the Nummuline series as Polytrema in 

 the Rotaline. As we are led from the typical Rotalia, through 

 the less regular Planorbulina, to Tinoporus, in which the cham- 

 bers are piled up vertically, as well as multiplied horizontally, and 

 thence pass by an easy gradation to Polytrema, in which all regu- 

 larity of external form is lost; so may we pass from the typical 

 Operculum or JSfummulina, through Heterostegina and Cyclocly- 

 peus to Orbitoides, in which, as in Tinoporus, the chambers 

 multiply both by horizontal and by vertical gemmation; and from 

 Orbitoides to Eozoon the transition is scarcely more abrupt than 

 from Tinoporus to Polytrema. 



The general acceptance, by the most competent judges, of my 

 views respecting the primary value of the characters furnished by 

 the intimate structure of the shell, and the very subordinate value 

 of plan of growth, in the determination of the affinities of Fora- 

 minifera, renders it unnecessary that I should dwell further on my 

 reasons for unhesitatingly affirming the Nummuline affinities of 

 Eozoon from the microscopic appearances presented by the proper 

 wall of its chambers, notwithstanding its very aberrant peculi- 

 arities ; and I cannot but feel it to be a feature of peculiar interest 

 in geological inquiry, that the true relations of by far the earliest 

 fossil yet known should be determinable by the comparison of a 

 portion which the smallest pin's head would cover, with organisms 

 at present existing. 



I need not assure you of the pleasure which it has afforded me 

 to be able to co-operate with Dr. Dawson and yourself in this 

 development of my previous researches ; but I may venture to add 

 the anticipation that the discovery of Eozoon is the first of many 

 discoveries in the Laurentian series, which will vastly add to our 

 knowledge of the primaeval life of our globe. And I am strongly 

 inclined also to concur in the belief expressed by Dr. Dawson in a 

 private letter to myself, that a more thorough examination of some 

 of the Silurian fossils (such as Stromatopora) hitherto ranked 

 among corals and sponges, will prove that they are really, like 

 Eozoon and Receptaciilitcs, gigantic Foraminifera. 



