ON DREDGING AMONG THE SHETLAND ISLES. 235 
Names of Species. Synonyms, 
Cadulus subfusiformis, Sars. 
Chiton Hanleyi, Bean. 
C. cancellatus, G. B. Sow. 
@F cinereus, Desa eile eclns ee es C. asellus, Sp. 
Glevis; Dlont:c apie rerr ec ote C. corallinus, Risso. 
Tectura virginea, Miill. 
Propilidium ancyloides, Ford. 
Scissurella crispata, Flemung ...... S. aspera, Ph., var. 
Trochus cinerarius, Z., var. variegata. 
Rissoa reticulata, Mont. .......... R. Beanii, Hanley. 
R. cimicoides, Fork. ......+..005 R. sculpta, Forbes § Haney, not of 
R. Zetlandica, Mont. Philippi. : 
R. abyssicola, Ford. 
R. parva, Mont., and var. interrupta R. obscura and R. simplex, Ph. 
R. inconspicua, Alder. 
Teall sees TG Pienieleinion pot oO Om re R. Oenensis, Brusina. 
R, vitrea, Mont. 
Jeffreysia diaphana, did........... Rissoa? glabra, Ald., not of Brown. 
Aclis Walleri, Jeffr. 
Odostomia clavula, Lov. 
O. albella, Zov. 
O. wmbilicaris, Malm. 
O. conspicua, Ald. 
O. Scillee, Seacchi. 
O. nitidissima, Mont. 
Eulima bilineata, A/d. 
Natica catena, Da Co oe. ccc eens Probably Nerita helicina, Brocche. 
Velutina levigata, Penn, 
Cerithium metula, Lov. ......606 Mediterranean, fide Hanley. 
Purpura lapillus, L. 
Trophon Mérchi, Malm .......... Bela demersa, Tiber. 
Bulla utriculus, Broccht .......... B. Cranchii, Leach. 
Philine scabra, Mill. ...........- Bullea angustata, Biv. 
Aplysia punctata, Cuvier.......... A. hybrida, J. Sowerby. 
Spirialis retroversus, FV........... Sczea stenogyra, Ph.; oceanic. 
Clio pyramidata, Z...........005- Oceanic. 
How is this concordance to be accounted for? I have carefully read again 
Forbes’s elaborate essay “On the Connexion between the distribution of the 
existing Fauna and Flora of the British Isles, and the Geological changes 
which have affected their area, especially during the epoch of the Northern 
Drift ” (Memoirs of the Geological Survey of Great Britain, vol. i. 1846) ; but 
TI cannot find in it a satisfactory solution of the question. He, indeed, men- 
tions the continuance of some “arctic” species in the British seas, the rest 
haying “retired for ever,” and that certain other species which he called 
“ Boreal or Celtic” occurred in a fossil state in Sicily; and he states (p. 390) 
that “in the deepest of the regions of depth in the Aigean ” the same repre- 
sentation of a northern fauna as exists in our own seas is maintained, “ partly 
by identical and partly by representative forms.” The instances he gives do 
not support such a view; and I am nota believer in “ representative forms.” 
He evidently was not aware of the fact that boreal (not arctic) species still 
live in the Mediterranean. I, however, fully agree with him that at some 
former period (which he designates “the newer pliocene epoch”) there was 
an open communication between the Atlantic (according to him the “ North 
Seas”) and the Mediterranean, by which the fauna became diffused. I 
should be inclined to place the Atlantic point of communication at Bordeaux, 
and that of the Mediterranean at Narbonne, in the line of the Languedoc 
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