10 CYCLOSTOMI: HYPEROABTIA. — III. 



Order HI. HYPEROAKTIA. 



Characters given above. One family only, (imepi^a, palate ; 

 ipTios, complete.) ; 



Family III. PETROMYZONTID^. (The Lampreys.) 



Body eel-shaped, naked, compressed behind ; mouth subcircular, 

 armed with horny teeth, which rest on papillae ; gill openings 7, 

 arranged in a row along the side of the " chest " ; lips present, 

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

 more or less notched ; intestine with a spiral valve ; eggs small. 

 The lampreys undergo a metamorphosis, the larva of all species 

 being toothless and having the eyes rudimentary. The name 

 Ammoccetes was formerly applied to the larval forms ; originally, 

 however, to that of A. branchialis. Genera 3 or 4, species about 

 15, chiefly of the fresh waters of temperate regions. They attach 

 themselves to fishes, and feed by scraping off the flesh with their 

 rasp-like teeth. 



a. Second doi-sal joined to the caudal. 

 b. Supraroral lamina ("maxillary tooth ") expanded laterally, forming a 

 crescent-shaped plate, with a cusp at each end, and sometimes a median 



cusp; anterior lingual teeth serrate Ammoccetes, 3. 



bb. Supraoral lamina contracted, of two or three teeth close together; discal 

 teeth numerous, in concentric series; buccal disk large (in adult, 

 very small in larva). ... ... Peteomyzon, 4. 



3. AMMOCCZiTIiS Dumeril. (ajijios, sand ; koItt), bed.) 



u. Supraoral lamina with a very small median cusp or none; edge of anterior 

 lingual tooth small, crescent-shaped, dentate, the median denticle en- 

 larged; buccal disk small, with few teeth. (Ammoccetes.) 



3. A. branchialis (L.). Mud Lamprey. Brook Lamprey. 

 Dorsal continuous, deeply notched, both parts high; about 8 

 bicuspid teeth on each side of buccal disk ; the other teeth sim- 

 ple ; infraoral plate with 5 to 9 blunt subequal cusps ; head with 

 gills 4| ; myocommas 6 7, between gills and vent ; an anal papilla 

 present in spring. Color bluish black. L. 8. Cayuga L. {Meek) 

 to Minn, and Ky., ascending brooks in spring. (.Eu.) (P. niger, 

 Raf., not of Lacepede.) (Lat., having gills.) 



4. PETROMTZON (Artedi) Linnseus. (n-trpa, stone; 



/nj'fm, to suck.) 



i». Anterior lingual tooth divided in two by a median groove ; dorsal fin con- 

 tinuous, with a broad notch. (Ichthyomyzon Girard.) 



4. P. castaneus (Girard). Supraoral lamina (maxillary tooth) 

 tricuspid ; some lateral teeth bicuspid ; infraoral lamina (mandib- 



