ON BRITISH MARINE ZOOLOGY. 249 
termination of the relative proportions of bivalves to univalves in ancient 
sea-beds, all mineral indications of the nature of the sea-bed being at the 
same time noted, we may get at an additional clue to the determination of 
the depth of the ancient sea in which such animals lived. 
The distribution of the sub-littoral forms of testacea, as shown by our 
dredging papers, may be illustrated by the following examples :— 
Certain species are common to the Laminarian, Coralline and Deep-sea 
Coral Zones, as— 
Psammobia ferroensis. Turritella communis. 
Syndosmya intermedia. Cerithium reticulatum. 
Venus striatula. Natica Alderi. 
' Venus cassina. Natica montacuti. 
Venus ovata. Nassa incrassata. 
Venus fasciata. Aporrhais pes-pelecani. 
Cardium suecicum. Buccinum undatum. 
Cardium fasciatum. Fusus antiquus. 
Lucina borealis. Fusus gracilis. 
Lucina flexuosa. Trophon Barvicense. 
Kellia suborbicularis. Clavatula linearis. 
Crenelle. Trichotropis borealis. 
Nuceule. Eulima distorta. 
Pinna ingens. Eulima subulata. 
Pecten similis. 
Some of them, under rare circumstances, as in a few localities (Skye and the 
lochs of Ross-shire) in the West Highlands, are found occasionally living at 
low-water. I have before called attention to this fact, and to the circum- 
stance that on the neighbouring shore in such localities the alpine plants 
descend from the mountains and are distributed along the water’s edge. I 
am strongly impressed with the suspicion that this curious phenomenon, so 
far as I have observed it, always seen in connexion with the neighbourhood 
of outliers of the glacial submarine fauna, has a relation, as yet unexplained, 
with the history of the changes in the configuration and elevation of land at 
the close of the glacial epoch. 
Certain species are common to Laminarian and Coralline Zones, and in- 
differently inhabit both, as-— 
Cyprea europea. Tellina donacina. 
Natica helicoides. Lucinopsis undata. 
Eulima polita. ἡ Lepton squamosum. 
Velutina laevigata. Lima hians. 
Mactra elliptica. Lima Loscombi. 
Artemis exoleta. Modiola modiolus. 
Artemis lincta. Ostrea edulis. 
Circe minima. Pecten varius. 
Certain species commence their range in the Coralline Zone, as— 
Rissoa abyssicola. Cerithium metula. 
Pleurotoma teres. Trochus alabastrum. 
Cemoria noachina. Fusus islandicus. 
Propilidium fulvum. Neera costellata. 
Pilidium ancyloides. Neeera abbreviata. 
Nucula tenuis. Leda pygmeza. 
Arca raridentata. 
rin it is curious to observe that all these are members of the Scandinavian 
auna. 
\ A few species appear to be confined to the region of deep-sea corals; as Apor- 
