43 
in, this position appear small, and more or less aborted. The margins of 
contiguous corallites, both in the imtliiclcened and thickened condition, arc 
often rendered uneven by the projection of the acanthopores inwards. In 
the first case they give to the wall a moniliform appearance, and in the 
second they render the inner outline of the corallite irregular, or fluctuating, 
and tend to still further obliterate any trace of the former polygonal outline 
the particular corallite may have possessed. Again, a parallel case may be 
seen in the figure of Geinitzella columnaris, ScliL, sp., given by Waagen and 
WentzcT. 
Messrs. Waagen and Wentzel have criticised" Prof. H. iV. Nicholson’s 
view that the acanthopores throughout the Monticuliporidse are peculiarly 
modified corallites.^ They regard them as newly-developed gerns,^ and remark 
as follows : — “ The figure quoted above shows us a number of these spiniform 
corallites within the central portion of the colony as compact dark spots 
without hollows in the middle. In the same figure, however, we see more 
towards the peripheral region of the colony, just where the transition between 
the central and peripheral regions takes place, these so-called spiniform coral- 
lites opening out and transforming themselves into little tubes. These again 
become more and more widened, and at last become corallites of the common 
shape. Prom these observations it appears, beyond doubt, that a great part 
of the so-called spiniform corallites are nothing but newly-developed gems.” 
In the late edition of his “ Pabnontology,” Prof. Nicholson has replied'^ 
to this, and I cannot do better than quote his words — “ Waagen has expressed 
the opinion that the ‘ acanthopores’ are only immature tubes, but this is con- 
clusively shown to be erroneous by the fact that, while immature tubes can 
be readily demonstrated in all specimens, the ‘ acanthopores’ are strictly 
confined to particular species of Monticuliporoids, and are uniformly absent 
in others. Moreover, they differ entirely in structure from the young tuljes, 
and, unlike the corallites (whether young or old), they project above the 
general surface of the colony in the form of spines. Again, when they are 
limited in number, the acanthopores occupy definite positions as regards the 
ordinary tubes of the colony ; and, finally, in many forms the acantho- 
pores are so numerous as to render the hypothesis that they are of the nature 
^ Pal. Indica, Salt Range Fossils, 1886, Vol. I, Part 0, t. 112, f. 4. 
* Pal. Indica, Salt Range Fossils, 1886, Vol. I, Part 6, p. 870. 
“ Genus Monticulipora, &c., 1881, p. 46. 
* i.e., young corallites. 
^ A Manual of Palteontology, &c. Third Edition. By H. A. Xicholson and R. Lydekker, 1889, I, p. 349. 
