Ch. XXI.] ' PELAGIC HTDEOZOA. K57 



marine insect Halobatis, the anomalous Pterosoma, with 

 every now and then little greyish-yellow swimming crabs 

 (Lupea pelagica), either side of whose carapace was deve- 

 loped into a long spine ; and several minute fish, among 

 them young flying-fish and Hemiramphi. 



Besides this assemblage of animals, Hydrozoa (jelly-fishes) 

 often abounded, more particularly pelagic species of the 

 orders Physophoridaq, of which the Portuguese man-of-war 

 (Physalia) is an example, and Lucemaridse or umbrella- 

 form Acalephs, like those thrown up on our own shores ; of 

 the former, perhaps, Velella, Physalia, and Porpita occur 

 more frequently than any others, and usually ia company 

 with one another — the first two especially seldom seen one 

 without the other. The Physaliae and Velellse look like large 

 bubbles as they drift by at a little distance, but their per- 

 sistence attracts attention, and their rich colours cannot fail 

 to strike the most unobservant, especially when of large 

 size. Exposing considerable surface to the wind, they sail 

 along with the faintest breeze, and in a gale are huddled 

 together in fleets, and, stranded in great numbers upon the 

 nearest shore. I saw thousands of both at the mouth of 

 Kelung harbour, Formosa, after bad weather. The Porpitse 

 are less common, but usually occur in considerable numbers 

 when seen at all — looking like beautiful and sharply-cut 

 gun-wads, witli delicate radiating markings, and surrotmded 

 with a fringe of deep-blue tentacles. The number of these 

 three forms of Hydrozoa must be enormous, and their range 

 very remarkable. I have found them extending over 55° of 

 latitude, and have no reason to believe this to be the limit. 



In lat. 12° N., near Socotra, and again in 5° N., near 

 Ceylon, I was not a little surprised to observe in great num- 

 bers a small fly of a yeUowish-brown coloiu-, hovering over 



