298 PISCES. 



very, blackish and olive on the backj first dorsal very distinct 

 from the second; two large separated teeth on the upper part of 

 the maxillary ring. Inhabits rivers, &c. 



P. planeri^ Bl.j iSucet, &c.; Gesner, 705. (Small River Lam- 

 prey.) From eight to ten inches longj teeth and colours of the 

 fluvialis; the two dorsals contiguous or united. Rivers, &:c.(l) 



Myxine, Lin. 



But a single tooth on the upper part of the maxillary ring, which is 

 altogether membranous; lateral dentations of the tongue strong, and 

 arranged in two rows on each side, so that the jaws of these fishes 

 seem to be lateral like those of Insects or the Nereides, which in- 

 duced Linnaeus to place them in the class of Vermes; the rest of 

 their organization, however, is analogous to that of the Lampreys:(2) 

 the tongue also acts like a piston, and the spine of the back is in the 

 form of a cord. The mouth is circular and surrounded with eight 

 cirri; in its upper margin is a spiracle which communicates with its 

 interior. The body is cylindrical, and furnished behind with a fin 

 that surrounds the tail. The intestine is simple and straight, but 

 wide and plaited internally; the liver bilobate. There are no 

 vestiges of eyes. The eggs become large. These singular animals 

 pour out such an abundance of mucus through the pores of their 

 lateral line, that the water of the vases in which they are kept seems 

 to be converted into a jelly. They attack and pierce other fishes 

 like the Lampreys. 



They are subdivided according to the external orifices of their 

 branchise. In 



Heptatremus, Dumer. 



There are still seven holes on each side, as in the Lampreys. 



But a single species is known, Gastrobranche dombey, Lacep., 

 I, xxiii, 1; Petromyzon cirrhatus^ Forster; Bl., Schn., p. 532; 

 from the South Seas. (3) 



1 ) N.B. The figure of the Planeri, Bl., 78, 3, is a young Jluvialis. I also 

 think that the Petrom. sucet, Lacep., II, i, 3; Sept-oeil, IV, sv, 1? Noir, lb., 2, 

 are mere varieties of the planeri: but the fig-. I, ii, 1, under the name of Lam- 

 proyon, Petrom. branchialis, represents a peculiar species of this genus, and not an 

 AmmoccEtes. I see no difference between the Petrom. argenieus, BL, 415, 2, and 

 the Jluvialis. 



(2) See the Memoir of Abildgaart, Trans. Soc. Nat. Berlin, vol. X, p. 193. 



(3) See the Memoir of Sir Ev. Home, Phil. Trans., 1815. 



