FAMILY PETROMYZONIDiE — PETROMYZON. 379 



ORDER III. CYCLOSTOMI. 



Gills purse-shaped, fixed, opening outwards by several apertures. Jaws represented by an 

 immovable cartilaginous ring, formed by the union of the palatine and mandibular bones. 

 Intestinal canal straight and narrow. 



Obs. The skeleton of the fishes of this order is very imperfectly developed ; so much so 

 that they are considered, and with justice, to be the most imperfect of all vertebrated animals. 

 It forms a small group, scarcely exceeding a dozen species. 



FAMILY PETROMYZONID^. 

 Body elongated, cylindrical, eel-shaped. No pectorals nor ventrals. Fins without rays. 



GENUS PETROMYZON. Linneus. 



Seven branchial apertures on each side of the neck. Maxillary ring armed with strong teeth. 

 Mouth beneath. 



THE AMERICAN SEA LAMPREY. 



FetROMTZON AMERICANU8. 



PLATE LXVI. FIG. 216. 



P.marinus, Sea Lamprey at New-York. SCHtEPFF, Beobachtungen, &c. Vol.8, p. 184. 



The Great Lamprey^ Petrtmiyzon marimts. MiTCHiLL, Trans. Lit. and Phil. Soc. Vol. ], p. 461. 



Petromyzon americanua. Lesuevr, Am. Phil. Soc. new series, Vol. 1, p. 382, 



P. id. Id. Hist. N. A. Fishes, ined. plate. 



The American Lamprey, P. id. Storer, Report on the Fishes of Massachusetts, p. 195. % 



Characteristics. Body olive-green mottled with dark brown ; ending behind in an acute tip. 

 Throat armed with three large teeth. Length two to three feet. 



Description. Head depressed, and with the mouth closed, obtusely conic ; a single tubular 

 orifice equidistant from, and slightly anterior to the eyes. Back subcarinate. A row of mu- 

 cous ducts on each side of the head, from the snout towards the eyes ; a row of from six to 

 eight before the eyes, and directed forwards ; another from the lower side of the mouth, rising 

 upwards towards the extremity of the snout ; a short series running backwards, from the su- 

 perior part of the orbits ; a distant scries along the back, on each side ; an indistinct unequal ' 

 row between each branchial aperture, and irregular groups and scries distributed over the 

 whole anterior part of the body. Mouth forming a longitudinal fissure, and when attached to 

 any thing, assumes the form of a regular circle. Teeth of various kinds, which may be con- 

 sidered as disposed in concentric circles about a common centre, or as arranged in somewhat 



