60 NATTTEAL HISTOEY SOCIETY OF DUEL2W. 



burning rays of the sun. The fish finds itself retained against its will; 

 the air bladder, becoming overdistended by the heat, resists the efforts 

 of the animal to compress it. It thus continues floating until the cool 

 of the evening condenses the air in the bladder, and restores the power 

 of descending. 



In Orthagoriscus, that possesses neither air bladder nor the power of 

 inflating the body, the small size of the pectoral fins, and the dorsal, 

 anal, and caudal fins, being merely organs of progression, it is natural 

 to infer that — like Pleuronectidce, or Flat-fish, and the Lophidm, or 

 Anglers — they have not the will nor the necessity to rise to the 

 surface, but more likely to remain near the bottom, where Crustacea, 

 Mollusca, and Corallines form their principal food. The Eays, which 

 have powerful pectoral fins, are enabled by their considerable action to 

 rise readily to the surface without the assistance of an air bladder. The 

 formation of the caudal fin or tail is of much importance in determining 

 the characteristic of the fish as to its swiftness or sluggishness of swim- 

 ming. Thus the rounded form of the mola, and the truncate character 

 of that of the oblongus, would prove them to be fish of slow movements. 

 However, we cannot form conclusive views upon the habits of these 

 ground-feeding fish ; the most we can arrive at must be suppositions 

 founded from observation on internal as well as external organization, 

 and deduction from analogical reasoning. 



One remarkable character, Mr. Swainson states, "that in the class 

 of fishes, the shape of the pectoral and caudal fins are almost always 

 symmetrical — that is, that the caudal fins are forked in the same propor- 

 tion as the pectorals are pointed; nor doe? an instance at this moment 

 occur to us where the pectoral fin is pointed and the caudal rounded, or 

 the contrary." Now it is very evident, in the instance of the oblongus, 

 there is a departure from the views advanced by Mr. Swainson. Again, in 

 the genus Pcecilia, of South America, a similar character is seen. Pcecilia 

 unimaculata, observed by Mr. Darwin in fresh-water ditches at Rio 

 Janeiro, and described in the zoology of the voyage of H. M. S. Beagle, 

 has the caudal rounded, while the pectorals are narrow and pointed. 

 Tetraodon angusticeps, inhabiting the Galapagos Archipelago, shows a 

 beautiful radiating bifurcating of the rays of the caudal fin, resembling 

 that of the oblongus. 



Since this paper has been drawn up, Mr. Robert Ball, Director of 

 the Museum in the University, has kindly informed me that in the Mu- 

 seum there is a specimen of the oblongus, which he suspects to have 

 been sent there, with several rarities of birds and fish fromWexford, by 

 the Rev. Mr. Elgee, about the year 1790. 



Dr. Scouler then commented upon the admirable state in which 

 Mr. Andrews had preserved the species of Sun-fish this evening 

 exhibited, and he congratulated the Society upon the higher grade 

 of views that Mr. Andrews had drawn of the characters and 

 analogies of that species, with the other, the Mola — statements so 

 superior to the mere describer of external form, or to the collector 

 or noter of habitats. He did not agree with what Mr. Andrews 



