954 REPORT—1850. 
gist will do well to bear in mind that entire well-marked generic groups of 
testacea are confined to, and indicute with certainty, the space between tide- 
marks and the sea-bed to a depth of about 15 fathoms below low-water mark. 
* Relation of colour to distribution Although the extent and depth of our 
seas scarcely afford sufficient data for illustrating the influence of light in the 
colouring of marine animals, yet some facts bearing on this subject may be 
gathered from the papers before us. In the horizontal diffusion of species, 
several, as some of-the Zrochi and Veneride, exhibit a distinct influence of 
light upon the brightness of their hues, in the south, as compared with the 
dull aspect of speeimens from the north, and this in individuals of the same 
species. It is easy for the practised conchologist to distinguish specimens of 
most painted shells, gathered on the southern coasts of England, from those 
taken on other parts of our shores. We have evidence also of the distinct 
effect of depth in the defacing of the hues of the same species, when it has a 
great bathymetrical range. Thus the examples of Venus striatula, Venus 
ovata and Turritella terebra (all having a range from the Laminarian zone to 
the deepest recesses of the British seas), taken alive at a depth of 100 
fathoms off the Zetland Isles by Mr. MacAndrew, were colourless ; whilst 
those from more moderate and shallow depths are almost always conspicu- 
ously coloured, Between 60 and 80 fathoms in the Scottish seas, dirty white, 
dull red, yellow or brown, rarely broken into stripes or bands, are the pre- 
vailing hues of the testacea ; though at 50 fathoms, shells painted in patterns 
and vividly coloured (as Natica Alderi and Clavatula purpurea), exhibit their 
hues unimpaired. At the same time it must not be forgotten that the vividly 
painted animal of the coral Caryophyllia thrives at a depth of 80 fathoms. A 
curious phenomenon apparently connected with depth is the blindness of the 
crustacean Calocaris. 
Condition of the exuvie of marine invertebrata taken in the dredge—lIn the 
great majority of instances and places, the dead shells of mollusca are taken 
nearly entire, or, in the case of the bivalves, with the valves disunited but 
not broken. ‘This applies especially to all localities of a considerable depth, 
and where strong currents are not in action. Very near the shore, broken 
shells are not uncommon ; and in current-ways, even at the depth of 30 
fathoms, the bottom may be composed in great part of triturated shells. 
Lieut. Thomas, R.N., observes, when communicating his lists of Testacea 
dredged around the Orkney Islands, that “ between Fair Island and the 
Orkneys, the bottom near the latter islands is either rocky or composed of 
large pieces of Modiola modiolus or Pectunculus glycimeris. I make no 
doubt,” he remarks, “that these are broken by some large species of Crus- 
tacea(?); their freshness of fracture is astonishing, as if the creature feeding 
had been disturbed at his meal.” Among bivalves, besides those mentioned, 
the shells of Thracia, Cyprina, Isocardia, and the larger species of Cardium 
are most frequently found broken; among univalves, those of Buceinum and 
Fusus. Some few bivalves are ‘frequently dredged dead, yet with their 
valves united; such are Zucina radula, the Neere, ‘Mactra elliptica, Psam- 
mobie, Venus ovata and striatula, Tapes virginea, Tellina donacina, Thracia 
phaseolina, Lucinopsis, Nucula pygmea, Solens, Syndosmye and Pectunculus 
pilosus, this last open and gaping. The monomyarious bivalves are often 
found dead in quantities, but almost always with valves disunited ; and this 
may be said of the great majority of dimyarious bivalves also. Echinoderms 
fall to pieces when dead, or if taken entire have lost their spines. 
Phenomena of the horizontal distribution of species on the western shores 
of Great Britain.—In the older accounts of British marine animals, the phrase 
“ from Devon to Zetland” was frequently given as marking their range, and 
