160 PLYMOUTH MARINE INVEETEBKATE FAUNA. 



PLYMOUTH SOUND AND THE ADJACENT TIDAL RIVERS. 



Plymouth Sound must be regarded as an enclosed and sheltered arm 

 of the sea, into wliich the two tidal rivers, the Taniar (with its estuary 

 the Hamoaze) on the west, and the Plym (with its estuary the Catte- 

 water) on the east, discharge their waters. The fauna and the flora of 

 the Sound, in their general nature, are marine rather than estuarine. 

 The typical estuarine species of the Hamoaze and Cattewater occupy 

 no predominant place in their composition, and the effect of the fresh 

 water entering the area does not appear to be great. On the other 

 hand the conditions in the Sound differ from those obtaining on the 

 open coast, chiefly in respect to the force of the action of the waves, 

 and possibly also to the degree of circulation of the waters, both being 

 greatly modified by the presence of the Breakwater. 



The fauna and the Hora of the Sound are comparable to those found 

 near the mouths of the different estuaries along the south coasts of 

 Cornwall and Devon : e.g. Salcombe Estuary below the Salstone (</. this 

 Journal, vol. vi. p. 151), Yealm Estuary below the junction of Newton 

 Creek with Yealm River. 



Shores of the Sound. 



No attempt will be made to give a detailed account of the whole 

 coast-line, but typical portions, which offer the best opportunities for 

 collecting, will be described. 



The shores of the Sound are for the most part rocky, with gravel and 

 stones between the rocks. Fine sand in small patches is exposed liere 

 and there at extreme low water, but there are no stretches of sandy 

 shore. 



Rum Bay. This term is used as a general name for the shore from 

 Batten Breakwater to Jennycliff' Bay.* It is a moderately sheltered 

 stretch of coast, with low rocks of a very friable shale, which dip 

 seawards and form ridges parallel to the line of coast. Near low-water 

 mark the ground between the rocks is for the most part very stony, but 

 fine sand and gravel are found at intervals. The low shale rocks are 

 covered, between tide-marks, with Fucus, Pclvctia, AscophyUnm, and 

 other brown weeds, occurring in definite zones, whilst at dead low 

 water Lnminarin is plentiful. The weeds and rocks are the home of 

 the usual shore Gastropods of the district {Purpura lapillus, Patella 

 vulrjata, Littorina neritoides, L. rudis, L. littoralis, Gihhnla cineraria, 

 G. umbilicata, Calliostoma zizyphinus, Ocinehra erinacea), occurring each 

 at its proper tidal level, as well as of the Polychretes Nereis pelagica 



* The teini Kiiin Vmy, as here used, includes both Batten Bay and Rum Bay of the 

 Admiralty charts. 



