Dr. Bancroft on the Sea-Devil of Jamaica. 447 



into action. It seems more natural to suppose that they might help to- 

 wards shifting his course to either side ; but the extent, the range of 

 action, and the power of his pectoral fins, are such as scarcely to require any 

 aid from the flaps for this purpose. I am accordingly assured by Lieute- 

 nant St, John, who has attentively watched the movements of the fish on 

 many occasions, that when he alters his course to one side, he changes 

 his body from its usual horizontal position, to an inclined one, keeping the 

 fin of the opposite side uppermost, and this he curves into a concave 

 form, so as, by holding water, to arrest his progress on that side, and 

 thereby make it serve as a kind of pivot on which to turn ; whereas the 

 flaps are only moved when the fish is as it were at rest, seeking his food. 

 He then brings them alternately in a lateral direction, from without in- 

 wards, and vice versa, presenting the flat surface towards the mouth, by 

 which he is enabled to drive a large volume of water into it at each 

 movement; and as the mouth itself is formed of strong rigid cartilages, 

 allowing of no motion whatever beyond simply opening and shutting, and 

 is firmly set besides into the shoulders or thorax, the flappers in question, 

 acting nearly as the mandibles of some tribes of insects, must doubtless 

 be of the utmost utihty to the animal in increasing his supplies of both 

 food and water. Their utility ceases, however, the moment he begins to 

 move, when, in order to lessen the obstruction to his advance which they 

 would cause, even if loose, he coils the flexible portion of each against the 

 ridge by a single oblique turn, into a straight roll, which stands perpen- 

 dicularly from, and out of his line of vision, so as at a certain distance to have 

 been taken for a pair of horns. By these explanations the contradictory 

 accounts that have ascribed ears, horns, lobes, wattles, &c. to the animal, 

 become reconcileable with each other and with truth. The singulariry of 

 the organ, its probable importance to the economy of the fish, and the 

 imperfect or mistaken ideas which were entertained as to its structure 

 and uses by those naturalists even who have constituted it an essential 

 character of their new genus, will, I hope, excuse the length of the fore- 

 going details. 



The body has some resemblance to a rhomb truncated at the apex, and 

 is depressed and convex on the upper surface, but rather less so on the 

 under. The anterior or truncated portion, or head, is furnished, at each 



