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G. W. Lee—Treposiomata. 
There are wide differences of opinion regarding the taxonomic value of the growth - 
shape in Bryozoa generally, and the difficulties encountered by workers on Mesozoic and 
Tertiary Bryozoa are also met with in the study of the Palaeozoic Trepostomata. Owing 
perhaps partly to the fact that suites of. complete zoaria are very difficult to obtain, thus 
often precluding the possibility of observing the merging of one growth-shape into 
another, the majority of workers seem to have agreed to give specific—even generic— 
value to the mode of growth. As, moreover, it has in several cases been shown to 
express systematic difference, it is safer to recognise it whenever the materials do not 
show transitional growth-shapes that would justify the merging of the forms. 
In the British fauna a very common type of purely individual variation is exhibited 
by many of the ramose species, which may be indifferently solid or hollow, the two modes 
sometimes co-existing in the same branch. It is interesting to note that this tendency is 
more pronounced in some species than in others. Stenopora redesdalensis and Tabulipora 
howsei exhibit it in a remarkable degree, while it does not seem to obtain in other species, 
for instance T. scotica. 
V.—Notes on the Genera. 
The species examined are referable to six genera. Future investigation may show 
some of these to be too comprehensive, while others may ultimately prove not to be true 
genera. But a certain degree of uncertainty in the generic divisions is at present 
unavoidable, the materials studied being in many cases too meagre to allow a satisfactory 
phylogenetic arrangement. 
Genus Stenopora Lonsdale. 
Lonsdale’s original diagnosis is as follows. “ A ramose, spherical or amorphous 
tubular polypidom ; tubes polygonal or cylindrical, radiated from a centre or an 
imaginary axis, contracted at irregular distances but in planes parallel to the surface of 
the specimens ; tubular mouths closed at final period of growth ; ridges bounding the 
mouths granulated or tuberculated ; additional tubes interpolated.” 1 Although this 
gives a faithful description of the external characters of most species of Stenopora, it is 
insufficient for the needs of modern palaeontology, since it was drawn up before the 
introduction of the use of thin sections. Lonsdale’s description was, however, good 
19, p. 2(32.. 
