470 I'ETROMY/ID.E. 



eyes, and gill-covers ; while the fish under consideration has 

 neither eyes nor gill-covers, nor any fins except one along 

 the back. 



Supported by the opinions of three or four zoological 

 friends, I have placed this little animal in this family, near 

 the cyclostomous fishes, believing it to be, as far as at present 

 known, the lowest in organization among this class ; and 

 although I am unwilling to mutilate entirely by my rough 

 dissection the only specimen probably I shall ever possess, 

 and which is perhaps unique, I shall yet be able to show, by 

 the figures given and some further description, that this 

 animal is entitled to a place at the end of the present 

 family. 



The form of the fish is compressed ; the head pointed, 

 without any trace of eyes ; the nose rather produced : the 

 mouth on the under edge, in shape an elongated fissure, 

 the sides of which are flexible ; from the inner margin ex- 

 tend various slender filaments, regularly disposed, which 

 cross and intermingle with those of the opposite side. Along 

 the sides of the body the muscles are arranged in regular 

 order, diverging from a central line, one series passing ob- 

 liquely upward and backward, the other series as obliquely 

 downward and backward : the anal aperture is situated one- 

 fourth of the whole length of the fish, in advance of the 

 end of the tail ; the tail itself pointed : from the nose to 

 the end of the tail a delicate membranous dorsal fin extends 

 the whole length of the back, supported by very numerous 

 and minute soft rays ; the surface of the body smooth. 



The body is strengthened and supported internally 

 throughout its length by a flexible cartilaginous column, 

 from which the numerous muscles diverge ; the cavity of the 

 abdomen is comparatively large ; the intestine a canal of 



