268 Proceedings of the Royal Physical Society. 



Thus, on the above views, we cannot account for double 

 refraction in a biaxal crystal if the ether be supposed incom- 

 pressible by the action of the material molecules. If, 

 however, the ether be supposed compressible, the equations 

 of motion are of a more general character, the discussion of 

 which will form the subject of a paper which the author 

 hopes shortly to publish elsewhere. 



IV. — (1.) Notice of the i: Etuet," a species of Tetraodon (Tetraodon 

 — — = ?) recently received from the Rtv. Alexander Robb, Old Calabar. 

 By John Alexander Smith, M.D. (The specimen was exhibited.) 



The following extract from a letter which I received from 

 the Kev. Alexander Robb, dated Creektown, Old Calabar, 

 28th October 1864, gives all the information about this 

 Tetraodon which I am able to lay before the Society : — 



" The fish is named Etuet by the natives of Old Calabar, 

 and possesses the power of inflating itself to an unusual 

 degree. I do not know whether it has been described, but 

 I think that it has been sent home. The Etuet is considered 

 dangerous as food ; but it is said that it can be eaten with 

 safety by the removal of a certain part of it." 



In March 1857, as noticed in the volume of our Proceed- 

 ings for that year, Mr Andrew Murray exhibited a species 

 of Tetraodon received from Old Calabar ; and gives the 

 following short account of its characters : — " It did not 

 correspond with any of the species described by Lacepede, 

 and was probably new. Instead of being armed with great 

 spines, it was nearly smooth, except on the belly, where it 

 was covered by a number of small prickles. It was dark 

 brown above, and pale beneath, and had a row of six deep 

 red spots along its sides. Mr Murray named it provisionally 

 Tetraodon pustulatus." 



This may probably be the specimen to which the Rev. 

 Mr Robb refers ; and the description of its colour, and the 

 spotted appearance of its sides, agree generally with the 

 one now exhibited. This one seems to differ, however, 

 from Mr Murray's specimen, in having apparently no spines 



