10 CYCLOSTOMI: HYPEROARTIA. III. 



ORDER III. HYPEROARTIA. 



Characters given above. One family only. ({/Trepwa, palate ; 

 aprios, complete.) 



FAMILY III. PETROMYZONTID^l. (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 

 Ammocoetes 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 dorsal 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) ........... PETROMYZON, 4. 



3. AMMOCOQTES Dumeril. (a/i/ior, sand ; KOITT/, bed.) 



a. 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 3 

 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. PETROMYZON (Artedi) Linnaeus, (rrerpa, stone ; 



fiv'a>, to suck.) 



a. 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- 



