70 Professor Edward Forbes on 



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 striatulay 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 Mac Andrew, were colourless ; whilst 

 those from more moderate and shallow depths are almost always 

 conspicuously coloured. Between 60 and 80 fathoms in the Scot- 

 tish seas, dirty white, dull red, yellow or brown, rarely broken into 

 stripes or bands, arc the prevailing hues of the testacea ; though at 

 50 fathoms, shells painted in patterns and vividly coloured (as Natica 

 AlderisiwA Clavatula purpurea), exhibit their hues unimpaired. At 

 the same time it must not be forgotten that the vividly painted ani- 

 mal of the coral Caryophyllia thrives at a depth of 80 fathoms. A 

 curious phenomenon apparently connected with depth is the blind- 

 ness of the crustacean Calocaris. 



Condition of the exuvicc of marine invertebrata taken in the dredge. 

 — In 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 com- 

 posed of large pieces of Modiola modiolus or Fectunculus glycimeris. 

 I make no doubt," he remarks "that these are broken by some 

 large species of Crustacea (?) ; their freshness of fracture is astonish- 

 ing, 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 Buccinum and 

 Fusus. Some few bivalves are frequently dredged dead, yet with 

 their valves united ; such are Lucina radida, the Necerce^ Mactra 

 eUiptica^ Psammobioi, Venus ovata and striatulay Tapes virginea, 

 Tellina donacina, Thracia phaseolina, Lucinopsis, Nucula pygmaja, 

 Solens, SyndosmycB, and Fectunculus pilosus, this last open and 

 gaping. The monomyarious bivalves are often found dead in quan- 

 tities, 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, aud the natural inference from such 



