R. Etheridge, jun.—Carboniferous Tubicolar Annelida. 307 
Peebles-shire (Mr. J. Bennie). Prof. G. A. Lebour informs me that 
this species is very characteristic of the 4 fathoms limestone, high up 
in the Northumbrian Carboniferous Limestone Series, at Denwick, 
near Alnwick. 
12. Serpulites membranaceus, M‘Coy. 
S. membranaceus, M‘Coy, Synop. Carb. Foss. Ireland, 1844, p. 170, t. 23, f. 31. 
Morris, Cat. Brit. Foss. 1854, 2nd ed. p. 93. 
Bigsby, Thes. Dev.-Carbonif. 1878, p. 243. 
Sp. char.—Tube elongate, curved, thin, more or less flattened, and 
membranaceous. Margins thickened; surface generally wrinkled. 
Obs.— Whether this will stand the test of future research as a 
species is, I think, doubtful. It appears to be separated from 8. 
carbonarius by such very trivial characters that I have doubts of its 
stability. Size apparently is the chief difference, between the two, 
although we have intermediate examples which bridge over the 
gap. If the size shown by M‘Coy’s figured example is a constant 
character, then probably S. membranaceus is a good species. On the 
other hand, we meet with examples of S. carbonartus of the typical 
size covering slabs of shale intermingled with flattened, bi-ridged 
tubes of much greater dimensions, and of several sizes, and possess- 
ing otherwise all the characters of the smaller tubes, which are 
undoubtedly S. carbonarius. If these are parts of one and the same 
organism, and there does not seem any reason to doubt it, then I do 
not see why the form, known as S. membranaceus, should not repre- 
sent the largest condition of growth. 
A slab of shale in the Museum of Practical Geology from Lesma- 
hagow has such a mass of tubes on its surface. The smallest of these 
measures nearly a line and a half in width, whilst the largest tube 
present is four lines broad. If, therefore, there is this marked 
difference between the extremes of portions of what are to all intents 
and purposes the same species, it is just possible M‘Coy’s S. membra- 
naceus may only represent an individual of still larger growth, 
notwithstanding that its width is six lines. The only difference 
between the latter and the form I am now referring to is the 
wrinkled integument, the latter being in the specimens quite smooth.! 
One strong point in the argument against the identity of S. carbona- 
rius and S. membranaceus lies in the fact that at certain localities, 
for instance, Teases Quarry, near Lundin, Fife, the former occurs in 
quantity, but always the small form, and of one uniform size. 
This question is one which can much more readily be settled by 
close examination in the field of large beds of these peculiar worm- 
tubes, and must for the present remain open. 
Loc. and Horizon.—Messrs. Armstrong and Young? give several 
localities at which S. membranaceus occurs, viz. Gair Quarry, near 
Carluke, in the Upper Carboniferous Limestone Group; in the main 
limestone of the Lower Carboniferous Limestone Group at Carluke, 
etc. 
1 In specimens from other localities, however, the surface is quite as much 
wrinkled as in M‘Coy’s S. membranaceus. 
' .2 Trans. Geol. Soc. Glasgow, iii. App. p. 23. 
(To be concluded in our next Number.) 
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