CHAP. 1V.] THE CRUISES OF THE ‘PORCUPINE, Ari 
eation of structure under altered conditions of life. 
Three specimens were procured on two different 
occasions, and they are in all respects similar. 
Mollusca are much more abundant and varied 
in the warm area than in the cold. Mr. Gwyn 
Jeffreys remarks, however, that there is not such 
a decided difference in the Molluscan fauna of the 
two regions as might have been expected from the 
difference in their conditions; very many species 
being common to both. At 500 fathoms the sponges 
are full of Pecten vitreus, CHEM., and Columbella 
halieti, JEFFREYS; and throughout the area species 
occur of many Molluscan genera, including Lima, 
Dacridium, Nucula, Leda, Montacuta, Axvinus, Astarte, 
Tellina, Neawra, Dentalium, Cadulus, Siphonoden- 
talium, Rissoa, Aclis, Odostomia, Aporrhais, Pleuro- 
toma, Fusus, and Buccinwin. 
Taken as a whole the fauna of the warm area off 
the north of Scotland seems to be an extension of 
a fauna with which we are as yet very imperfectly 
acquainted, occupying what we must now call 
moderate depths, say from 300 to 800 fathoms, 
along coasts which are bathed by currents of equa- 
torial water. The fauna of this zone is evidently 
extremely rich; and as it is beyond the reach of 
ordinary dredging from an open boat, and yet not 
at_ a sufficient depth to present any very great diffi- 
culty from a yacht of average size, its exploration 
seems to present just the combination of adventure 
and novelty to stimulate amateurs; so we may 
hope shortly to have its conditions and distribution 
cleared up. A most successful step in this direction 
has been made already by Mr. Marshall Hall, who 
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