ON DREDGING AMONG THE SHETLAND ISLES. 235 



Names of Species. Synonyms. 



Cadulus subfusiformis, Sars. 

 Chiton Hanleyi, Bean. 

 C. cancellatus, G. B. Sow. 



C. cinereus, L C. asellus, Sp. 



C. lasvis, Mont C. corallinus, Rlsso. 



Tectura virginea, Mull. 

 Propilidium ancyloides, Forb. 



Scissurella crisp^ata, Fleming S. aspera, Ph., var. 



Trochus cinerarius, L., var. variegata. 



Rissoa reticulata, Mont R. Beanii, Hanley. 



R. cimicoides, Forb R. sculpta, Forbes $ Haney, not of 



R. Zetlandica, Mont. Philippi. 



R. abyssicola, Forb. 



R. parva, Mont., and var. interrupta R. obscura and R. simplex, Ph. 



R. mconspicua, Alder. 



R. albella, Lov R. Oenensis, Brusina. 



R. vitrea, Mont. 



Jefireysia diaphana, Aid. Rissoa ? glabra, Aid., not of Brown. 



J. opalina, Jeffr. 



Scalaria Trevelyana, Leach. 



Aclis Walleri, Jeffr. 



Odostomia clavula, Lov. 



O. albella, Lov. 



O. umbilicaris, Malm. 



O. conspicua, Aid. 



O. Scillse, Scacchi. 



0. nitidissima, Mont. 



Eulima bilineata, Aid. 



Natica catena, Da C. Probably Nerita kelicina, Brocchi. 



Vehitina laevigata, Penn. 



Cerithiuni metula, Lov Mediterranean, fide Hanley. 



Purpura lapillus, L. 



Trophon Mb'rchi, Malm Bela demersa, Tiberi. 



Bulla utriculus, Brocchi B. Cranchii, Leach. 



Philine scabra, Mull. Bulltea angustata, Biv. 



Aplysia punctata, Cuvier A. hybrida, J. Soiverby. 



Spirialis retroversus, Fl. Scaea stenogyra ; Ph. j oceanic. 



Clio pyramidata ; L 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. 18.46) ; but 

 I 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 

 having " 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 JEgean " 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 not a 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 



