FAMILY PETROMYZONID — PETROMYZON. 379 
ORDER UI. CYCLOSTOMI. 
Gulls purse-shaped, fined, 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. 
Ors. 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 PETROMYZONIDL. 
Body elongated, cylindrical, eel-shaped. No pectorals nor ventrals. Fins without rays. 
GENUS PETROMYZON. § Linneus. 
Seven branchial apertures on each side of the neck. Maaillary ring armed with strong teeth. 
Mouth beneath. 
THE AMERICAN SEA LAMPREY. 
PeETROMYZON AMERICANUS, 
PLATE LXVI. FIG. 216. 
P. marinus, Sea Lamprey at New-York. Scua@prrr, Beobachtungen, &c. Vol. 8, p. 184. 
The Great Lamprey, Petromyzon marinus. Murcuitt, ‘Trans. Lit. and Phil. Soc. Vol. 1, p. 461. 
Petromyzon americanus. Lrsurur, Am, Phil. Soc. new series, Vol. 1, p. 382. 
P. id. Ip, 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 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, which may be con- 
sidered as disposed in concentric circles about a common centre, or as arranged in somewhat 
