FAMILY PETROMYZONID^ — PETROMYZON. 379 



ORDER III. CYCLOSTOMI. 



Gills purse-shaped, fixed, opening outwards hy 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 PETROMYZONIDJE. 

 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. 



PeTROMTZON AMERICiNUS. 



PLATE LXVI. FIG. 216. 



P. marimts. Sea Lamprey at Neio-York. ScHOSPFF, Beobachlungen, &c. Vol. 8, p. 184. 



The Great Lamprey, Petromyzon marinus. MiTCHILi, Trans, Lit. and Phil. Soc. Vol. 1, p. 4P1. 



Petromyzon americamis. Lesdedk, 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 si.x 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 series along the back, on each side ; an indistinct unequal 

 row between each branchial aperture, and irregular groups and series 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, v/hich may be con- 

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



