Petromyzontidæ.

Body eel-shaped, naked. Subject to a metamorphosis. In the perfect stage with a suctorial mouth armed with teeth simple or multicuspid, horny, sitting on a soft papilla. Maxillary, mandibulary, lingual, and suctorial teeth may be distinguished. Eyes present (in mature animals). External nasal aperture in the middle of the upperside of the head. The nasal duct terminates page 95 without perforating the palate. Seven branchial sacs and apertures on each side behind the head. The inner branchial ducts terminate in a separate common tube. Intestine with a spiral valve. Eggs small.

The larva; without teeth and with a single continuous vertical fin. Mordacia mordax. Tasmanian rivers "Lampreys."

——geotria australis. Tasmanian rivers "Lampreys."

Inhabitants of the fresh waters and coasts of the temperate regions of both hemispheres. Suck themselves fast to other fish, and live by scraping off their flesh. (Günther.)