40 MEMOIR III. 



possessed of tliis curious property, viz. medusa pelluccns 

 of Sir Joseph Banks, (Philos. Trans. 1810, pi. XIV, fig. 3) 

 and the medusa Spallanzanii not hitherto figured ; both of 

 these belong to tlie genus Aurelia of Lamarck, of which 

 we have many species not luminous. 



The third kind of luminosity, (C) is comparatively of 

 rare occurrence, and that which is the most alarming in 

 appearance ; I had but once an occasion to witness and 

 to investigate it as it occurs in the Mediterranean. Return- 

 ing from a fishing party late in a still evening across the 

 bay of Gibraltar, in a direction from the Pomones river 

 to the old Mole, in company with Dr. Drummond, (now 

 Professor of Anatomy to the Belfast Institution) and a 

 party of naval officers, the several boats, although se- 

 parated a considerable distance, could be distinctly traced 

 through the gloom by the snowy whiteness of their course, 

 while that in which we were, seemed to be passing 

 through a sea of melted silver 5 such at least was the 

 appearance of the water, displaced by the movement of 

 the boat and the motion of the oars ; the hand, a stick, 

 or the end of a rope, immersed in the water, instantly 

 became luminous and all their parts visible, and when 

 withdrawn, brought up numerous luminous points less 

 than the smallest pin's-head, and of the softest and most 

 destructible tenderness, ajipearing on a closer inspection 

 out of the water, like hemispheric masses of a colourless 

 jelly, evidently however, organized and included within 

 an enveloping tunic j these were probably some species 

 of minute medusa. This appearance however, is proba- 

 bly caused by several different animals ; thus the animal 

 discovered by Mr. Langstaff on a voyage from New 

 Holland to China, appears to have been the linked young 

 of some Salpa, Avhile that observed by Riville is undoubtedly 

 a crustaceous animal of the ostracoda. The former, as 

 cited by Professor Macartney in his valuable paper on 

 luminous animals, (Philos, Tra?is. 1810;) states " In going 



