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AMONGST THE CORALS OF THE PALOZOIC PERIOD. 245 
It is obvious, namely, that a fasciculate corallum, similar, for example, to that 
of Lithostrotion irregulare, may very readily be produced by the repetition of 
the fissiparous process, provided only that the fission involve but a portion of 
the parent calice,—that the original corallite continues to grow, and that the 
new corallite extend itself in a direction approximately parallel to that by which 
it was produced. In the same way, fission is perfectly capable of producing a 
massive astreiform corallum, perfectly similar in its appearance to one which 
may owe its form to calicular gemmation. Without entering here into further 
details as to these perplexing resemblances, it need only be added, that the case 
is not uncommonly complicated. by the coexistence of fission with gemmation in 
the same coral. 
II. CLASSIFICATORY VALUE OF THE MOopE or GROWTH. 
Under this head we have to consider what value is to be attached to the 
mode of growth of the corallum from a purely systematic point of view; and I 
hope to be able to show that its importance has been generally over-rated, so 
far at any rate as fossil corals are concerned. It has, namely, been generally 
assumed that difference in the mode of growth is to be regarded as being at 
least of generic value, and not a few genera are based essentially upon this 
alone. In the case of recent corals, where we are acquainted with the soft parts 
of the actinosoma, the mode of growth is doubtless a most important help to 
arriving at a correct classification. In the case, however, of fossil corals, where 
we must be guided solely by the nature of the skeleton, there appear to be good 
reasons for believing that too much stress has been laid upon the mere mode of 
growth. 
a. In the first place, there is often extreme difficulty in the case of fossil 
corals in determining what the mode of growth actually may be. Two instances 
will be sufficient to exemplify this. Thus, the genera Chetetes, Fischer, and 
Monticulipora, D’Orbigny, include a number of corals which are in most respects 
precisely similar, being composed of closely aggregated polygonal, circular, or 
sub-circular corallites, traversed by well-developed tabulee, with imperforate 
walls, and either without septa, or with these structures in a very rudimentary 
condition. The sole distinction by which the two genera are separated is, that 
the corallum of Chetetes, as redefined by LonspALE and M‘Coy, and as accepted 
by Mitne-Epwarps and Haine, is stated to increase by the subdivision or 
fission of the tubes ; whereas the mode of growth in Monticulipora is stated to 
be by gemmation. This distinction, however, is one which it is extremely dif- 
ficutl, if not impossible, to apply in practice. The truth of this remark is shown 
by the fact, that the msot eminent paleontologists have arrived at precisely 
opposite conclusions as to the mode of growth of the same species. Mr 
