Class MARSIPOBRANCHII. 



The Lampreys and Hagfishes. 



Skeleton cartilaginous; skull not separate from the imperfectly 

 segmented vertebral column; no true jaws; no limbs; no shoulder 

 girdle; no pelvic elements, and no ribs; gills purse-shaped, without 

 gill arches; 6 or more gill openings on each side; nostril single, on top 

 of the head; heart without arterial bulb; alimentary canal straight, 

 simple, without ccecal appendages, pancreas, or spleen; naked, eel 

 shaped animals. 



Order Hyperoarfii, 



Nasal duct a blind sac not communicating with the palate; mouth 

 nearly circular, suctorial ; seven gill openings on each side of the neck. 



Family i. Petroiiiyzoiiidsp. 



The Lampreys. 



Body eel-shaped, somewhat compressed posteriorly; mouth nearly 

 circular, suctorial, and armed with horny, tooth-like, simple or multi- 

 cuspid tubercles; those just above and below oral opening, and those 

 on tongue more or less specialized; lips or margin of mouth fringed. 

 A. Supraoral cusps 2 or 3, placed close together; dorsal fin with 

 a broad notch. Ichihyomyzon, 231 



AA. Supraoral cusps 2, each at end of a crescent-shaped plate; oc- 

 casionally a rudimentary median cusp; dorsal fin with sharp 

 notch. Lampetra, 23 



o 



Genus Ichtliyoiiiyzoii Girard. 



River Lampreys. 



Supraoral plate, with 2 or 3 cusps placed near each other; anterior 



lingual tooth with a median groove; dorsal fin with a broad shallow 



notch. Small lampreys inhabiting lakes and rivers of eastern United 



States. 



231 



