200 MR. HOLDSWORTH ON THE DISTRIBUTION OF CORALS. [JunC 24, 



the British Museum are several specimens of this coral which were 

 brought from Sicily. These are all attached to a species of Turri- 

 tella. The occurrence of this second species of Caryophyllia in 

 three distinct localities on our coasts entitles it to a place among our 

 British corals ; and further investigation will probably show it to be 

 generally distributed in the deep water along our western shores. 



It may not be uninteresting to inquire here into the distribution 

 of corals around the British Islands, and to trace, as far as possible, 

 the cause of their frequenting only particular lines of coast. 



The existence of the coral-polype in our seas is mainly dependent 

 on the warmth and purity of the water. A tolerably high tempera- 

 ture is undoubtedly one of the most necessary conditions for the well- 

 being of the delicate polypes whose calcareous lamellated skeletons 

 constitute the true stony corals. Only within the tropics do we meet 

 with those, vast reefs and extensive accumulations of coral-growth 

 which form so characteristic a feature of the seas in those warm lati- 

 tudes. The surface-water there becomes heated by the direct influ- 

 ence of the sun, and, in those regions, few coral-polypes carry on 

 their ceaseless work at a greater depth than 30 fathoms, thence 

 building upward to the lowest tide-mark. As we come towards more 

 temperate regions, the species diminish both in size and number ; 

 simple forms become proportionately more numerous, and their ba- 

 thymetrical range is greatly increased. 



The waters of north-western Europe might be expected generally 

 to be too much within the influence of Polar temperature to be fitted 

 for coral-life, even in its simplest form ; yet in our own seas, and 

 extending far into the Arctic Ocean, are found some few species 

 vying with the productions of the Tropics in brilliancy of colouring 

 and delicacy of structure. Here, however, we have a peculiar and 

 extraneous source of warmth in the Gulf Stream, whose waters, now 

 becoming widely diifused, but still retaining some portion of their 

 original excessive temperature and motion, exercise a sensible influ- 

 ence on the coast-productions of the western side of the British 

 islands. The course of the current in the neighbourhood of our 

 shores is marked sparingly, but distinctly, by the presence of eight or 

 ten species of living coral. 



The long list of habitats recorded by Mr. Gosse in his valuable 

 ' Actinologia Britannica' has been of great use to me in tracing the 

 range of our native species ; and although many parts of the coast 

 have been but little worked, enough has been done to furnish a 

 tolerably clear outUne of the distribution of the coralligenous polypes. 

 From the writings of Maury and others, it appears that the Gulf 

 Stream is divided by the British Islands ; one portion going south- 

 ward to the Bay of Biscay, the other and main body of the current 

 sweeping away to the north by the Orkneys and Shetland. The 

 entrance of the English Channel and the Irish Sea would thus be 

 under the most direct influence of the warm current ; and it is in these 

 waters we find corals most abundant. Devonshire and Cornwall are 

 extremely rich in these productions ; and, including Weymouth Bay 

 (the only recognized locality for Hoplangia durotrix), the south- 



