FAMILY PETROMYZONID^ — I'ETROMYZON. 379 



ORDER 111. CYCLOSTOMI. 



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

 immouahlc cartilaginous ring, formed hi/ the union of the palatine and mandibular bones. 

 Intestinal canal straight and narrow. 



Obs. The skeleton of the fislies of this order is very imperfectly developed; so niuch so 

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

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



FAMILY PETROMYZONID^. 



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



GENUS PETROMYZON. Linneus. 



Seven branchial apertures on each side of the 7icck. Maxillary ring anned with strong teeth. 

 Mouth beneath. 



THE AMERICAN SEA LAMPREY. 



Petromyzon americancs. 



PLATE LXVI. FIG. 210. 



p. marinus. Sea Lamprey at New-York. ScHCEPFF, Beobachtungcn, &c. Vol. 8, p. 181. 



The Great Lantprcy, Petromyzon marimiS. MiTCHILL, Trans. Lit. and Phil. Soc. Vol. 1, p. 4C1. 



Petromyzon atJiericanus. Lesueur, Adi. Phil. Soc. new series, Vol. 1, p. 392. 



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



The American Lamprey, P. id. Storer, Report on the Fi.shes of Massacliusctts, p. 195. * 



Characteristics. Body olive-grccn 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 die eyes ; a row of from six to 

 eight before the eyes, and directed forwards ; anodier from the lower side of the luoiitli, 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 liie 

 whole anterior part of the body. Jloudi 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 



