CHECK LIST OF THE 



Class MARSIPOBRANCHII. (The Lampreys.) 



Skeleton cartilaginous ; the skull imperfectly developed, not separate 

 from the vertebral column. No true jaws, no limbs, no shoulder girdle, 

 no pelvic elements, no ribs. Gills in the form of fixed sacs, without 

 branchial arches, six or more in number on each side. Nostril single 

 median. Mouth sub-inferior, suctorial, more or less circular. Heart 

 without arterial bulb. Alimentary canal straight, simple, without caecal 

 appendages, pancreas, or spleen. Vertical fins with feeble rays, usually 

 continuous round the tail. Naked, eel-shaped animals inhabiting cool 

 waters. They undergo a metamorphosis, the young being often quite 

 unlike the adult. 



Order HYPEROARTII. (The Lampreys.) 



Nasal duct a blind sac, not penetrating the palate. 



FAMILY PETROMYZONID^E. (THE LAMPREYS.) 



Body el<-shaped, subcylindrical anteriorly, compressed behind ; mouth 

 ys circular, armed with horny teeth which rest on papillae; gill open- 

 ngfs g&rfrt, -arranged in a row along the side of the "chest" ; lips present, 

 usually fringed ; nostril on top of head, just in front of eyes ; dorsal fin 

 more or less deeply divided by a notch; the posterior part commonly con- 

 tinuous with the anal around the tail ; intestines with a spiral valve ; eggs 

 small. 



The Lampreys undergo a metamorphosis, the larvae of all species 

 being toothless and having the eyes rudimentary. 



They attach themselves to fishes and feed by scraping off the flesh 

 with their rasp-like teeth. 



GENUS ICTHYOMYZON. 



Lampreys with the supraoral lamina armed with two or three separate 

 teeth, pointed and close together, not forming a crescent-shaped plate ; 

 anterior lingual tooth divided by a median groove. The dorsal fin notched 

 but not separated into two portions. 



