120 CORALS. MEDUS.E. — LUMINOSITY OF THE OCEAN. [OHAF. vi. 



CORALS. 



A few species of the tribe of corals are fished up from great 

 depths. Amongst the most remarkable are the Gorgoniaver- 

 rucosa, Sol., having a stem which forms the axis of an outer 

 calcareous coat; its cells are on both sides of the stem, which 

 branches out in a fan-shape form. These corals are often 

 covered with an elegant bivalve shell, the Avicula Mr undo, 

 Var., Aculiata. There is another coral, which has a delicate 

 scarlet hue for some time after it is taken out of the water ; 

 but as the colour depends on the animal tissue, it disappears 

 when this undergoes decomposition. 



MEDUSA. 



Star-fish, sea hedgehogs, and sponges are found on the 

 coast. The Caravel, or Portuguese man-of-war, which Sir 

 Hans Sloane described as Urtica marina, solnta, purpuria, 

 oblonga, cirrhis longissimis, with the delicate pink and blue 

 tints of their tiny transparent sails, sometimes cover the 

 waters of the bay like floating soap bubbles. Humboldt 

 mentions as having seen off Madeira the Medusa aurita of 

 Baster, the Medusa pelagica of Bosc, &c, with eight ten- 

 tacula (Pelagia denticuluta, Peron), and a third species, 

 which he says " resembles the Medusa hysocella, and which 

 Vandelli found at the mouth of the Tagus. It is known 

 by its brownish yellow colour, and by its tentacula, which 

 are longer than the body. They are sometimes four inches in 

 diameter, and their changeable colours of violet and purple 

 form an agreeable contrast with the azure tint of the ocean." 



LUMINOSITY OF THE OCEAN. 



Sir Joseph Banks, on his passage from Madeira to Rio de 



