268 
SUPPLEMENT TO THE BRITISH 
Length 1 inch 8 Hnes ; breadth about the same ; depth of its valve at its most 
convex part near the apex 4 lines. 
Obs. — If we leave out of account the still uncertain Discina ? Bechettiana from the 
Wenlock Limestone, the largest supposed species of Discina hitherto discovered would be 
the shell under description ; it exceeds in size B. Babeana, d'Orb. — D. Townshendi, 
Forbes, from the Rhsetic formations both of England and France. In external shape 
the free valve of B. Craigii bears much resemblance to 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 J), nitida which I am acquainted. 
Two examples were found by Robert Craig, Esq., of Langside, near Beith, in Ayrshire, 
at Dockra, close to the horizon from which the weathered-out shells were obtained which 
we have already described. 
6. Discina nitida, VUllips. Dav., Carb. Mon. p. 197, PI. XL VIII, figs. 18—25; 
Sup., PI. XXX, figs. 12, 13. 
Colour is of rare occurrence among Palaeozoic fossils ; Mr. John Young, of Glasgow, 
has recently detected remains of colour-markings on a specimen of Biscina nitida from 
Boghead Quarry, near Hamilton. Many specimens of this Biscina from the same locality, 
as observed by Mr. Young, are of a dark-blue colour, as in the case of B. Koninchii from 
the Permian limestone of East Thickley, near Darlington ; others are of a greyish white, 
but he met with only one specimen (Sup., PI. XXX, fig. 12) in which the two colours 
alternate in radiating form from the apex of the upper or unattached valve. I have also 
a specimen of the recent Biscina stella, Gould, dredged by Captain St.-John in the 
Straits of Korea, radiately striated as in the fossil species under notice. I likewise give 
a figure of a very remarkable interior of the attached valve of Biscina nitida, from the 
Carboniferous Limestone of Arden Quarry, near Glasgow, and cabinet of Mr. James 
Armstrong. In this example the muscular impressions are displayed in a very beautiful 
manner (Sup., PI. XXX, figs. 13, 13 a). 
Genus Crania, Betzius. 
7. Crania quadrata, M'Co?/. Dav., Carb. Mon., p. ]94, PI. XL VIII, figs. 1—13. 
It is well known that the unattached valve of this species is perforated by minute 
canals, which are visible in most cases with a pocket lens. It had been supposed that 
