2930 



LOWEST VERTEBRATES AND THEIR ALLIES 



all speed to the sea. The river lamprey was at one time thought to be a permanent 

 inhabitant of fresh waters, but it has been taken in the sea, and it has even been 

 considered that it may undergo its metamorphosis 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 quan- 

 tities in many of the English rivers, upward 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. 



In the Southern Hemisphere the family is represented by three 

 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 con- 

 tinuity 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 



Southern 



Lampreys 



HAGFISH. 

 (Three fifths natural size.) 



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 Ayres 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 



