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 ol 
which will form the subject of a paper which the author 
hopes shortly to publish elsewhere. 
IV. — (1.) Notice of the Etukt," a species of Tcfraod an [T air aodon. I 
— - ?) 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 i 
the Eev. Alexander Robb, dated Creektown, Old Calabar, j 
28th October 1864, gives all the information about this j 
Tetraodon which I am able to lay before the Society : — j 
" The fisli is named Etuet by the natives of Old Calabar, 1 i 
and possesses the power of inflating itself to an unusual i 
degree. I do not know whether it has been described, but i 
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 i 
brown above, and pale beneath, and had a row of six deep ■ 
red spots along its sides. Mr Murray named it provisionally ; 
Teti-aodon pustidatus." \ 
This may probably be the specimen to which the Kev. 1 
Mr Eobb refers ; and the description of its colour, and thej 
spotted appearance of its sides, agree generally with the 
one now exliibited. This one seems to differ, however, 
from Mr Murray's specimen, in having apparently no spines f 
