LAMPREYS AND HAG-FISHES. 
553 
morphosis in salt water. Always restricted to low-lying countries, this lamprey 
may be found alike in rivers, streams, lakes, and marshes, although it only spawns 
where the water is clear and flows swiftly over a stony bed. During the spawning- 
season, which takes place in March and April, the lampreys acquire a brilliant 
metallic lustre; while at the conclusion of the function they generally perish. 
Formerly these lampreys occurred in enormous quantities in many of the English 
rivers, upwards of three thousand having been taken at Newark in a single night; 
but the numbers in the Thames are now considerably diminished. Their chief use 
is as bait for cod and other fish; for which they are specially adapted on account 
of the ease with which they can be kept alive. There is nothing calling for special 
notice with regard to the habits of the small lamprey. 
Southern In the Southern Hemisphere the family is represented by three 
Lampreys, genera, in one of which there is a single species (Mordacia mordax ) 
common to the coasts of Chili and Tasmania; while in a second ( Geotria ) there is 
one Chilian and another South Australian species. The first of these two genera 
agrees with the typical representatives of the family in the continuity between 
the second dorsal and caudal fins, but differs in having two groups of three-cusped 
teeth above the aperture of the mouth; whereas in the second genus the two fins 
above-mentioned are separate, and there is a four-lobed plate above the mouth. 
Some of these lampreys grow to a length of a couple of feet; and in the adults of 
some or all of them the skin of the throat is so much expanded as to form a kind 
of pouch. The third genus ( Exomegas ) appears to be known only by two 
examples from the Atlantic side of South America, one of which was picked up 
in the streets of Buenos Aires in 1867, while the second was obtained from the 
Bay of Monte Video in 1890. With the exception that the dentition is of a 
peculiar type, very little is known as to the structure of this rare form. It will 
not fail to be noticed that the remarkable geographical distribution of these 
southern lampreys is paralleled by that of certain fresh-water fishes already 
described, with the exception that there is no instance among the latter where 
a species is common to Australia and South America. 
The hag-fishes, of which there are two genera, constitute a 
H s family (Myxinidce) distinguished from the last by the nasal sac 
having a posterior duct which perforates the palate; the single external nasal 
