Lamprey, a cyclostome or marsipobranch fish of the family petromyzonidce (hyperoartia, Muller), and genus petromyzon (Linn.). This order, with the myxinoids, constitutes the class of myzonts of Agassiz. The blood is red, the heart distinct, the branchial artery without a bulb and furnished at the base with two valves; the body smooth, cylindrical, and vermiform; mouth anterior, gills fixed, and eyes distinct; the single olfactory cavity opens above by an external foramen, leading to a blind canal not communicating with the mouth through a perforated palate as in the myxinoids; thorax cartilaginous, sustaining the branchial apparatus composed of rib-like strips descending on each side beneath the skin, with seven external spiracles, opening from the fauces into a sub-cesophageal tube, having a posterior caecal extremity. These are the first fishes in which there is a distinct brain enclosed in a cartilaginous cranium; there are two dorsal fins, the posterior joined with the caudal, and mere folds of skin with scarcely perceptible rudimentary rays; pectorals and ventrals absent; the cephalic cartilage is undivided; there is a spout hole on the head, and a spiral valve in the intestine; there is no oviduct nor seminal duct.

The jaws are absent, but the circular mouth, tongue, and pharynx are armed with conical or crescentic sharp teeth of indurated albumen. The gills are seven little fixed bags, each having its proper artery, its opening into the sub-cesophageal tube, and its external foramen by which the water passes out. - The old genus petromyzon has been subdivided into six, according to the shape and arrangement of the teeth. The common European lamprey, or lamprey eel as it is often called (P. marinus, Linn.), attains a length of more than 3 ft.; the color is yellowish marbled with brown. Having no air bladder and being destitute of lateral fins, they are usually found near the bottom, and to avoid being carried away by the currents they attach themselves to stones by means of the tongue, which acts like a sucking piston in the circular mouth, whence the names of petromyzon and cyclostomes; in the same manner they attach themselves to larger fishes, which they devour; by means of the apparatus above described, respiration may be carried on independently of the mouth, the branchial currents passing from one series of openings to the other across the sub-cesophageal tube.

The intestine is small and nearly straight; the eggs are laid late in the spring, the milt and roe escaping by a membranous sheath communicating with the abdominal cavity. They ascend rivers from the sea to spawn. They are very generally distributed in Europe from the Mediterranean to the arctic waters, ascending the rivers in spring; at this season great numbers are caught, their flesh being considered a delicacy. The food of the lamprey consists of any soft animal matter, especially the flesh of fishes to which they attach themselves. The river lamprey or lampern (P. fluviatilis, Linn.) is a smaller fish, and confined to fresh or brackish water; the length is from 12 to 18 in., and the color bluish olive above and silvery below. Great numbers were formerly caught in the Thames, Severn, etc, and sold to the Dutch for bait in the turbot fishery. This and the preceding species are very tenacious of life, living several days out of water. - The most common of the American species is the P. America-nus (Lesueur), growing about 2 1/2 ft. long; the color is olive brown above, with blackish brown confluent patches, and beneath uniform dull brown.

This is not uncommon in the rivers of New England and New York, especially near their mouths; it likes best shallow rapid streams with pebbly bottoms, in which it builds circular nests 3 or 4 ft. in diameter and a foot or two high, bringing stones in the mouth varying from the size of a hen's egg to that of the fist. They ascend high falls by clinging to the rocks, after suddenly darting forward; though uncommon in rivers obstructed by dams, they are abundant at their outlets, especially in the Merrimack near Lowell. Several other species are described in Dr.

Lamprey (Petroinyzon Americanus).

Lamprey (Petroinyzon Americanus).

Storer's "Synopsis of the Fishes of North America." - The genus ammoccetes (Dumeril) has the same cylindrical body, branchial apertures, and fins as the lampreys; the mouth is semicircular, without teeth, the posterior lip transverse and serrated within; the branchial apertures open internally into the oesophagus itself; the incomplete circle of the mouth prevents its adhering to rocks and other bodies; the external branchial openings are placed in a longitudinal furrow. It is often called mud lamprey, from its being found in the mud and sand. The best known species in Europe is A. branchialis (Cuv.), 6 or 7 in. long, about as thick as a goose quill, generally of a yellowish brown color above, darker on the head and back, lighter beneath; the eyes are very small; it spawns at the end of April, and feeds upon worms, insects, and dead matter, living in fresh water in many countries of Europe. Dr. Storer describes three species as occurring in North America, the A. bicolor (Lesueur), A. concolor (Kirtland), and A. unicolor (De Kay). From its resemblance to the lamprey, ammoccetes was called petromyzon by the early writers.

Aug. Midler (in his Archiv, 1856) maintains that ammoccetes is the larval form of petromy-zon, and does not attain the perfect state until the fourth year from the egg; subsequent observations confirm this view, which, if true, is a remarkable instance of partial metamorphosis in fish, and shows upon what transitory characters genera may be founded. According to Van der Hoeven, the cleavage of the yolk is entire, and in the first stage of development there is much analogy with that of the frog.