BRYOZOA FROM NEW ZEALAND. 



41 



enabled to make such direct comparisons with most of the recent 

 New-Zealand and Australian Bryozoa, making preparations of the 

 covers and other parts, and, during the three years that these collec- 

 tions have been in my hands, have been preparing myself for dealing 

 with the fossils by studying the recent forms. 



There are some people who think it is possible to turn aside from 

 other work and off-hand decide on the correctness of an author's 

 interpretation ; but, certainly with such a group as the present, 

 criticism such as every author ought to be glad to receive can only 

 be of value when the spirit of the work is entered into after pro- 

 longed examination. On this account it is much to be regretted 

 that there are so lamentably few workers on fossil Bryozoa, whereas 

 there are numbers of entirely new fields, and all the older work 

 ought now to be revised from our present stand-point in classi- 

 fication. 



The genus Membranipora, which is largely represented from near 

 Napier, is not one of the most useful paheontologically, because (1) 

 the shape of the oral aperture is never preserved, but only that of 

 the opesial aperture, which is of but secondary diagnostic value ; and 

 (2) in this genus the appearance of the zocecia is remarkably modified 

 by the presence of ovicells, but these are often wanting both in 

 recent and fossil specimens. In fact, among the recent forms, the 

 ovicells are not known in one half of the species, and even in some 

 of the commonest, such as M. pilosa, they have not yet been found. 



It will be seen from a reference to figures 2 and 5, 3 and 6 how 

 very different the appearance in various parts of the same colony 

 may be ; and this is by no means confined to the genus Membranipora, 

 but occurs in numerous genera, an example of which may be seen 

 in different parts of Microporella elevata, T.-Woods (see Quart. 

 Journ. Geol. Soc. vol. xli. pi. vii. figs. 6 and 9). 



In nearly all the commoner species with wide -geographical range, 

 such as Microporella ciliata, Cribrilina radiata, Rhynchopora hi- 

 spinosa, Cellejpora coronopus, Cribrilina monoceros, Porella concinna, 

 &c, the mode of growth, the thickness, the structure of the shell, 

 the size and number of spines*, the position of avicularia, and other 

 characters are known to be liable to great variation, causing the 

 appearance to be quite different. Yet notwithstanding this wide 

 range in common species, it seems to be overlooked that the same is 

 likely to be the case in species with which we are less acquainted ; 

 and the comparisons that I have been obliged to make in studying 

 the characters of the fossils have convinced me that not only by 

 those fresh in the field, but also by some of our most competent 

 workers, local varieties, or even specimens, have in many cases 

 been described as species. With the paucity of fossil material, it is 

 impossible that this can always be avoided, but I would urge the 

 advisability of more frequently indicating the relationships. 



I have never been satisfied as to the separation of Smittia and 

 Mucronetta ; and although we seem on the right track with regard to 



* Thus we have Membranipora Lacroixii and M. monostachys with and without 

 spines. 



