J. R. Dakyns — Glacial Origin of Terraces. 
17 
After comparing several Scottish specimens of this fine Lingula 
with Russian examples from Reval, given to me by Prof. F. Schmidt, 
I arrived at tbe conclusion tliat the specimens found by Mrs. Gray 
in the Caradoc Limestone at Craigliead Quarry, near Girvan, in Ayr- 
shire, belonged to the Russian species. The surface is marked with 
concentric strise, while along the middle of the shell may be observed 
obscure longitudinal lines. L. quadrata, as found in Russia, attains 
dimensions equalling if not exceeding those of the shell we have 
described as L. Canadense, but our Scottish examples do not quite 
attain to those dimensions. 
4. Discina Craigii, n. sp. PI. II. Figs. 1, In. 
Upper or free valve very thin and marginally nearly circular, 
about as broad as long, broadly rounded anteriorly, slightly less so 
posteriorly, conoidal and of moderate elevation : vertex sub-mar- 
ginal ; valves slightly flattened along the middle ; surface marked 
with fine concentric, slightly raised irregulär lines of growth, with 
very fine radiating strirn seen more or less distinctly here and there 
over its shining and bighly polished surface. Lower or pedicle 
valve not known. Length 1 inch 8 lines ; breadth about the same ; 
depth of valve at its most convex part near the apex 4 lines. 
Obs . — If we leäve out of account the still uncertain, so-termed 
Discina ? Beclcettiana from the Wenlock Limestone ? ; the largest 
British species of Discina hitherto discovered would be the shell 
under description ; it exceeds in size D. Babeana, D’Orb., = D. 
Townshendi, Forbes, from the Rhastic formation both of England and 
France. In external shape the free valve of D. Craigii bears much 
resemblance to that of D’Orbigny’s species, but differs from it on 
account of the flatness along the longitudinal middle of the valve. 
It is fully three times larger than the largest specimen of D. nitida 
with which I am acquainted. A single example was found by Robert 
Craig, Esq., of Langside, near Beith, Ayrshire, in the Carboniferous 
Limestone of that locality. 
Figs. EXPLANATION OF PLATE II. 
1 — 1 a Discina Craigii, n. sp. Carboniferous Limestone, Beith. 
2 — 3 Lingula quadrata, Eichwald. Caradoc Limestone, Craighead Quarry, Ayrshire. 
4 — 4 a Lingula Canadensis, Billings ? Llandeilo, Balcletchie, near Girvan, Ayrshire. 
5 — 6 Siphonotreta Scotica, n. sp. ? Caradoc Limestone, Craighead Quarry, near 
Girvan, Ayrshire. 
7 — 12 /Siphonotreta uuguiculata. 7. Internal cast, nat. size, Lower Silurian, Reval, 
Russia; 8. cast of larger or ventral valve enlarged ; 10. cast of dorsal valve, 
id. ; 9. interior of ventral valve ; 1 1. of dorsal valve ; 12. longitudinal section 
to show the position of the foramen. 
IY. — The Supposed Glacial Origin of Carboniferoes Terraces . 1 
By J. R. Dakyns, Esq. ; 
Of H. M. Geological Survey of England and Wales. 
T HERE is a homely saying, “ Sauce for the goose is sauce for the 
gander.” Hr. Goodchild, with that ingenuity for which he is 
remarkable, has written an elaborate paper to prove that the terraces 
of the Yorkshire Limestone dales are all the work of the Great Ice 
1 This paper was dashed off immediately after reading Mr. Goodehild’s paper, 
though not forwarded tili now. 
DECADE n. — VOL. IY. — NO. I. 
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