Marine Fauna of Great Britain. 403 



considerable numbers at the mouths of such salmon-rivers as 

 the Tay — and a few porpoises. The rorquhal and lesser 

 rorquhal are occasionally seen, and also scattered pairs of 

 the ca'ing whale. Killers are rare. 



Turning now to the extreme west, to shores more or less 

 influenced by warm currents both of air and water, the first 

 feature of note is the comparatively small rise and fall of 

 each tide, and, in bays like Lochmaddy, the great abundance 

 of mud ; but it must not be thought that the latter is absent 

 from the eastern shores, for a great deposit occurs east of the 

 Island of May and at many other parts of the coast. Before 

 proceeding to tlie consideration of the fauna of tlie west, we 

 may, indeed, glance briefly at this deposition of mud, a 

 question which has often been before marine zoologists. 

 Thus, during the ' Porcupine ' Expedition of 1870 Dr. Car- 

 penter broached the idea that the deposit of fine mud in the 

 deeper parts of the basin of the Mediterranean was devoid of 

 life because of the turbidity of the bottom-water. He held, 

 indeed, that such fine particles diffused through the water 

 would produce asphyxia in the marine animals. Further, he 

 pointed out the bearing of his explanation in regard to the 

 vast azoic deposits of the geologists. I showed at the time * 

 that such a theory should only be built on well-ascertained 

 facts, and, moreover, that, so far as my experience went, the 

 facts were not favourable. For example, many littoral 

 sponges are found on extremely muddy ground, while the 

 siliceous sponges all over the world affect a muddy bottom. 

 Muddy ground is the favourite haunt of zoophytes, sea-pens, 

 and other Coelenterates. Certain starfishes and Synaptce are 

 found only in mud. Terehellce and Gephyrea in vast numbers 

 are characteristic of muddy beaches ; not only these, but 

 many other annelids, are found nowhere else than amongst 

 mud or muddy sand, and this is often of such a nature that 

 the sea-water which covers them must always be loaded with 

 minute particles, which may also coat the littoral sea-weeds. 

 Some of the most delicate and beautiful of these annelids, with 

 the finest branchial plumes, live amongst tenacious chalk- 

 mud, yet they are so sensitive to other impurities that a very 

 slight admixture of fresh water is instantly fatal. Those 

 familiar with the habits of the shore-crab [Garcinus mcenas) 

 will be cautious in attributing a deleterious influence to mud 

 of any description. Others of the higher crustaceans burrow 

 in it. In muddy sand various raollusks live and thrive, such 

 as iScrohicuIariaj Corhula^ Crenella^ and even an occasional 

 oyster ; while ascidians and mussels are not only powdered 

 * Ann. & Mag. Nat. Hist., January 1872, p. 10. 



