1864.] CAKPENTEE — STRTJCTUEE OP EOZOON. 65 



Silurian rocks, shown by Mr. Salter's drawings* to be a gigantic Or- 

 bitolite, attains a diameter of 12 inches ; and if this were to increase 

 by vertical as well as by horizontal gemmation (after the manner of 

 Tinoporus or Orhitoides) so that one discoidal layer would be piled on 

 another, it would form a mass equalling Eozo'dn in its ordinary di- 

 mensions. To say, therefore, that Eozo'dn cannot belong to the 

 Foraminifera on account of its gigantic size, is much as if a Botanist 

 who had only studied plants and shrubs were to refuse to admit a 

 tree into the same category. The very same continuous gemmation 

 which has produced an Eozomi would produce an equal mass of 

 independent Glohig evince, if, after eight or ten repetitions of the pro- 

 cess, the new segments were to detach themselves. 



It is to be remembered, moreover, that the largest masses of 

 Sponges are formed by continuous gemmation from an original Rhi- 

 zopod segment ; and that there is no a priori reason why a Forami- 

 niferal organism should not attain the same dimensions as a Poriferal, 

 — the intimate relationship of the two groups, notwithstanding the 

 difference between their skeletons, being unquestionable. 



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

 Eozo'dn 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 liotalia, yet no less 

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

 among the Millepores. And it appears to me that Eozo'dn takes its 

 place quite as naturally in the NiimmuUne series as Polytrema in the 

 liotaline. As we are led from the typical Potqlia, through the less 

 regular Planorhulina, to Tinoporus, in which the chambers are j)iled 

 up vertically, as Avell as multiplied horizontally, and thence pass by 

 an easy gradation to Polytrema, in which all regularity of external 

 form is lost, so may we pass from the typical Operculina or Nummu- 

 Ihui, through Heterosteglim and Cycloclypeus, to Orhitoides, in which, 

 as in Tinoporus, the chambers multiply, both by horizontal and by 

 vertical gemmation ; and from Orhitoides to Eozo'dn 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 tJie very subordinate value of 

 plan of growth, in the determination of the aflftnities of Foramini- 

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

 reasons for unhesitatingly affirming the Nummuline affinities of 

 Eozo'dn from the microscopic appearances presented by the proper 

 wall of its chambers, notwithstanding its very aberrant peculiarities ; 

 and I cannot but feel it to be a feature of peculiar interest in geolo- 

 gical 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 



* First Pecade of Canadian Fossils, pi. x. 



VOL. XXI. — PART I. r 



