﻿J. R. Dahjns — Glacial Origin of Terraces. 17 



After comparing several Scottish specimens of this fine Zingula 

 with Eussian examples from Eeval, given to me by Prof. Y. Schmidt, 

 I arrived at the conclusion that the specimens found by Mrs. Gray 

 in the Caradoc Limestone at Craighead Quarry, near Girvan, in Ayr- 

 shire, belonged to the Eussian species. The surface is marked with 

 concentric strige, while along the middle of the shell may be observed 

 obscure longitudinal lines. L. quadrata, as found in Eussia, attains 

 dimensions equalling if not exceeding those of the shell we have 

 described as Z. Canadense, but our Scottish examples do not quite 

 attain to those dimensions. 



4. DisoiNA Craigii, n. sp. PI. II. Figs. 1, la. 

 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 irregular lines of growth, with 

 very fine radiating stride seen more or less distinctly here and there 

 over its shining and highly 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 leave out of account the still uncertain, so-termed 

 Discina2 Beckettiana from the Wenlock Limestone?; the largest 

 British ^species of Discina hitherto discovered would be the shell 

 mider description ; it exceeds in size T). Babeana, D'Orb., = D. 

 Toionsliendi, Forbes, from the Eheetic formation both of England and 

 France. In external shape the free valve of D. Graigii 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 B. nitida 

 with which I am acquainted. A single example was found by Eobert 

 Craig, Esq., of Langside, near Beith, Ayrshire, in the Carboniferous 

 Limestone of that locality. 



Figs. EXPLANATION OF PLATE II. 



1 — 1 a Biscina 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 Siplionotreta Scotica, n. sp. ? Caradoc Limestone, Craighead Quarry, near 



Girvan, Ayrshii-e. 

 7 — 12 Siphonotreta unguicidata. 7. Internal cast, nat. size, Lower Silurian, Eeval, 



Eussia; 8. cast of larger or ventral valve enlarged ; 10. cast of dorsal valve, 



id. ; 9. interior of ventral valve ; 11. of dorsal valve ; 12. longitudinal section 



to show the position of the foramen. 



IV. — The Supposed Glacial Origin of Carbonifekous Terraces.^ 



By J. E. Dakyns, Esq. ; 



Of H. M. Geological Survey of England and Wales. 



THEEE is a homely saying, " Sauce for the goose is sauce for the 

 gander." Mr. 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 



' This paper was dashed off immediately after reading Mr. Goodchild's paper, 

 though not forwarded till now. 



DECADE II. VOL. IV. — NO. I. 2 



