168 riA'MOUTH MARINE INVERTEBRATE FAUNA. 



both of iiidividtuils and of species. The same shore Gastropoda are found 

 ill their respective tidal zones, and the ledges of rocks and under sides of 

 stones are covered with the same species of sponges, ascidians, polyzoa, 

 anemones, and hydroids. Of echinoderms the representative species, as 

 on the siiores of the Sound, are Amphmra elegans, Ophiothrix fragilis 

 Echinus miliaris, and Cucumaria saxicola, all of which are found under 

 stones, tlie two latter only at extreme low water. 



Reny Rocks. A reef of exposed, weed-covered, low rocks running 

 from the Shagstone to the mainland. The fauna resembles that of the 

 rocks in Wenibury Bay. 



Whitsand Bay. An exposed shore which consists chiefly of fine 



shifting sand of a not very productive character. At intervals small 



reefs of low rocks run out amongst the sand, which form the home of 



a few ordinary rock-haunting species, and are specially characterised 



in places by the great abundance of the reef-building polychcete, 



Sahellaria alveolata. The rocky foundation in close proximity to an 



abundant supply of sand evidently furnishes to these worms the special 



conditions necessary for the formation of their masses of sand-built 



tubes. 



Dredging and Trawling Grounds. 



Cawsand Bay. Depth 3-5 fms. A characteristic inshore shallow 

 bay with a bottom of fine sand. Being sheltered from the south-west, 

 it is protected from the most violent and frequent gales, which in this 

 district come from that direction, and is only visited by lieavy seas 

 during gales from the east. In the shallowest parts of the bay is an 

 extensive bed of Zostcra, with a characteristic fauna, this being one of 

 the chief features which distinguishes the trawling grounds of Cawsand 

 Bay, from those of the more exposed Whitsand Bay, to be presently 

 mentioned. 



The smaller Crustacea {Hiiipohjte varians, Macromysis fiexuosa, 

 Cumacea, etc.) are abundant, and specimens of Maia squinado, the 

 common edible crab {Cancer jMgurns), mid the shrimi^ (Crangonvnlgaris) 

 are generally obtained. Sepiola atlantica is always present and often 

 numerous, and in the summer months Se2na officinalis is often abundant. 

 On the Zostcra, small specimens of Anemonia sulcata are frequent, and 

 Foraminifera, especially Polystomella crispa and Discorhina rosacea, are 

 generally abundant. Nassa reticulata occurs in quantity, often covered 

 with Hydroids. Spisula elliptica and Ensis ensis are common buried in 

 the sand. 



The most characteristic feature of the fauna of this bay is, however, 

 the fishes, which are not dealt with in the present report. These 

 consist of llat-fishes (.Soles, Plaice, Dabs, etc.). Skates and Eays, and 

 several species of pipe-fish. 



