25 
was generally supposed, and in support of this view he gave particulars of 
six well-known British Mollusca, each of which varied greatly in its 
bathymetrical range. 
1. Venus Casina, found ia the Newer Pliocene deposits, and generally obtained 
living from the zone of deep water (about 50 fathoms) which girdled the British 
Isles, had been taken in the Mull of Galloway, in 145 fathoms, and by Mr. 
Jordan off the Cornish coast in 50 fathoms, in Milford Haven in 6 to 10 fathoms, 
while on the little island of Hern, opposite Guernsey, it might be found living on 
the shore among the Zostera Marina. 
2. Buccinum undatum, was taken in our deepest water, by the Shetland cod- 
fishermen in 60 to 80 fathoms ; it was also readily obtained by the dredge, and 
found half buried in sand at low spring-tides. 
3. Terehratula caput-serpentis, like all Brachiopods, inhabited the deep sea, 
but in the Firth of Clyde might be dredged in a few fathoms, while Rev. M. J. 
Berkeley had found it between tide marks on the coast of Scotland. 
4. Cyprina Islandica, essentially a Boreal species, and abundant in the boulder- 
clay, inhabited the deepest water in the North seas, but further South it was found 
in shallower water, and in Swansea and Carmarthen bays was taken at low-water 
mark. Mr. Jordan considered that the probable reason of its living in shallower 
wafer as it ranged Southward, was that cold water was its proper habitat, and he 
inferred that the temperature of the Mediterranean sea, during the glacial epoch, 
was about the same as the present temperature of the British seas. 
5. Trochus ziziphemis, occurred at low-water mark at the Channel Islands, 
was dredged usually in the Laminarian zone, and had been taken in 80 fathoms 
by Mr. Jeffreys. 
6. Pectunculus glycimeris, abundant in the Coralline crag, generally considered 
characteristic of 30 to 50 fathoms depth. Mr. Jordan had dredged it in Milford 
at from 15 to 4 fathoms, and it abounded so greatly at Jersey at low-water mark, 
as to be used as an article of food. 
Mr. Jordan alluded to several other species, and observed that this in- 
teresting phenomenon of deep-water shell-fish living in the Littoral zone, 
was not confined to Mollusca, and drew the following conclusions from 
what had been stated — 
1. ''That bathymetrical range does not influence the distribution of Molluscan 
and Crustacean fauna so much as the nature and condition of the sea bottom, 
wherever these are highly favourable, species probably become gregarious." 
2. " That geologists cannot even approximately, much less definitely, determine 
the depth at which fossiliferous strata were deposited, solely on Palseontological 
evidence." 
In the second part of his paper, Mr. Jordan pointed out, from illustra- 
tions taken from the Mollusca of the Channel Islands, that great care was 
necessary in attributing older age to some tertiary strata than others, 
simply on Palseontological grounds, as Sir Charles Lyell had done in co- 
ordinating foreign and British tertiaries, wishing to show that the Diestian 
sands and Bolderburg beds of Belgium were older than the Coralline Crag 
D 
