specimens of the same type; for in them we find the superfi- cial cells differentiated from the intermediate layers (Fig. 21, <u>a</u>) precisely as in <u>Orbitolites</u>.<sup>X</sup> Looking to the far larger dimensions which these fossils present (S83) as compared with the existing spe- cimens of <u>Orbiculina</u>, <s>and to the fact that they are</s> I am dis- posed to believe that this <s>genus</s> type attained its highest develop- ment <s>at the</s> in a period long since passed; and that we now have, so to speak, only the degenerate descendants of <s>the</s> an ancestry of higher rank; whilst in the case of <u>Orbitolites</u>, I am <s>disposed</s> inclined to think that the type is most fully evolved at the present time. 91. <u>General Conclusion</u> - From the foregoing details it is obvious that the relationship between <u>Orbitolites</u> and <u>Orbiculina</u> is ex- tremely close; the only essential point of difference between them being that which is furnished by the structure of the nucleus. Whether <u>or not</u> they ought to rank as types of <u>distinct genera</u>, or whether they ought (as Prof. Williamson main tains) to rank as <u>cognate species</u> of the same genus, is a point as to which it is impossible to arrive at a satisfactory con- clusion, until the characters which should serve for the dis- tinction of genera and species in this class shall have been <s><u>rightly</u></s> determined on a physiological basis. This much I think myself entitled to assert with confidence, - that even if they are regarded as distinct genera, they must be - - - - - - - - X Although Mr Carter has described this fossil as a species of <u>Orbitolites</u>, yet it is really an <u>Orbiculina</u>, as is shown by the spiral conformation of its central portion (Fig.25), and by the in- vestment afforded by each turn of the spire to its predeces- sor, as shown in Fig.24<u>a</U>.
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Part 2: Researches on the Foraminifera, 1856. From The Royal Society, PT/53/8
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