FISHES 25 



ascend the streams to breed. The young animals, which are called 

 Ammoccetes, are without functional paired eyes, suctorial mouth or 

 teeth and pass through a metamorphosis; they live in this larval condi- 

 tion two to six years, during which they burrow in muddy bottoms in 

 the streams where they are born, feeding on minute organic particles 

 which the current brings them. Several of the smaller species have 

 apparently a very short adult life; the intestine is degenerate and non- 

 functional and the buccal teeth are weak, blunt and more or less 

 obsolescent; such species are probably not parasitic. 



Key to the United States Genera of Petromyzonidae 



El Buccal funnel with numerous teeth which radiate from the 

 mouth in all directions (Fig. 10). 

 bi Dorsal fin continuous; Great Lakes and Mississippi Valley. 



Ci Expanded buccal funnel much broader than body i. Icthyomyzon. 



Co Expanded buccal funnel narrower than body 2. Reighardina. 



b-2 Two separated dorsal fins; Atlantic slope 3. Petromyzon. 



32 Buccal funnel with teeth which do not radiate from the mouth 

 but lie in several groups (Fig. 12). 

 bi A posterior row of small teeth connect the posterior pair of 

 enlarged lateral teeth (Fig. 12). 



Ci Pacific Coast and Slope forms 4. Entosphenus. 



Co Atlantic Slope forms 5. Lethenteron. 



hi No such row of teeth present (Fig. 13). 



Ci Pacific Slope forms 6. Lampetra. 



Co Atlantic Slope forms 7. Okkelbergia. 



1. Ichthyomyzon Girard. Small fresh water lampreys with a single 

 dorsal fin which has a broad notch in the middle and is joined with the 

 caudal fin; muscle segments between gill and anus less than 60: i species. 



/. concolor (Kirtland). Silver lamprey. Length 300 mm.; color 

 silvery; a small dark spot above each gill pore; supraoral lamina with i 

 to 4 (usually 2) approximated cusps; buccal funnel, when expanded, 

 much wider than the body, and with a double row of marginal fringes: 

 valleys of the Great Lakes and St. Lawrence River; southward and 

 westward into the Ohio, Missouri and upper Mississippi valleys; 

 northwards to Hudson Bay; common on the sturgeon and other large 

 fishes. 



2. Reighardina Greaser and Hubbs. Similar to Icthyomyzon, 

 but with a narrow buccal funnel: i species. 



R. unicolor (DeKay) (Fig. 10). Length 150 mm.; supraoral lamina 

 with 2 separated cusps; buccal funnel, when expanded, not wider than 

 the body, and with weak or obsolescent teeth; intestine degenerate 

 in the adult: basin of the Great Lakes; often abundant. 



