('LASS MAESIPOBRANCHII — THE HAGEISHES AND LAMPREYS 



Class MARSIPOBRANCHII 



THE HAGFISHES AND LAMPREYS 



Skull imperfectly developed, not separate from the vertebral column; 

 no true jaws, no limbs, no shoulder girdle, no pelvic elements, and no ribs; 

 gills in the form of fixed sacs, purse-shaped, without branchial arches; nostril 

 single. Naked, eel-shaped animals, with a suctorial mouth, inhabiting 

 both fresh and salt water. 



Order HYPEROARTII 



the lampreys 



Nasal duct not penetrating the palate. This order is equivalent to the 

 single family Petromyzonidce, which follows. 



Family PETROMYZONIDi^E 



THE LAMPREYS 



Limbless, eel-shaped, naked-skinned vertebrates of parasitic or modi- 

 fied parasitic habit, with a circular suctorial mouth furnished with cusp- 

 like teeth suited for rasping; body subcylindrical forward, vertically flat- 

 tened behind; skeleton wholly cartilaginous; skull imperfect, continuous 

 with the vertebral column; no shoulder girdle, no pelvic elements, and no 

 ribs; vertical fins with feeble rays, ordinarily continuous around the tail; 

 gills 7 in number on each side, in the form of fixed sacs, and without true 

 branchial arches, being supported by a wicker-like arrangement of carti- 

 lages known as the "branchial basket"; gill-openings separate, arranged in 

 a row along each side of neck; nostril single, median, in front of eyes, the 

 nasal tube not penetrating the palate; mouth suctorial, without true jaws; 

 interior of buccal funnel (mouth disk) armed with horny teeth or tooth-like 

 tubercles, these being simple or multicuspid and resting on papillae; teeth 

 immediately above and below oesophagus (on the so-called ''tongue") more 

 or less specialized; heart without arterial bulb; alimentary canal straight, 

 simple, without csecal appendages, pancreas, or spleen; intestine with a 

 spiral valve; air-bladder wanting; generative outlet peritoneal, the eggs 

 small and falling into the abdominal cavity; young undergoing a meta- 

 morphosis, the larvae being blind and burrowing in the mud or sand. 



These remarkable creatures are among the most peculiar in 

 our waters, — peculiar in appearance, in habits and behavior, in 



