PETROMYZID.E. 



Supported by the opinion of Mr. Gray, and two or three 

 other 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 pre- 

 sent 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 

 considerable calibre, without convolution ; above it a double 

 row of flattened globular bodies, which have all the appear- 

 ance of ova. The figure at the top of the illustration re- 

 presents this fish of the natural size. The right-hand figure 

 in the middle line is an enlarged representation of the 



