FISHES 



25 



with sharp rasping teeth; bordering the mouth anteriorly and posteriorly, 

 respectively, are the so-called supraoral and injraoral lamince, horny 

 plates each with 2 or more teeth; intestine with spiral valve; 7 pairs of 

 gill-sacs, the external openings forming a row immediately back of the 

 eyes: about 15 species, in fresh and salt water; i family, the Petro- 

 myzonidae with about 8 species in the United States. 



Adult lampreys, in the case of most of the species, feed by attaching 

 themselves to fishes and sucking their blood 

 and rasping away the flesh, often killing them, 

 and causing large sores and scars on those they 

 do not kill; they are often destructive to fisheries. 

 The marine species ascend the streams to breed. 

 The young animals, which are called A mmocoetes , 

 are without functional paired eyes, suctorial 

 mouth or teeth and pass through a metamorpho- 

 sis; they live in this larval condition 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 nonfunctional 

 and the buccal teeth are weak, blunt and 

 more or less obsolescent; such species are probably not parasitic 



Fig. 10. — Buccal funnel of 

 I chthyomyzon unicolor (from 

 Jordan's Guide to the Study 

 of Fishes, after Gage). 



Key to the United States Genera of Petromyzonidae 



ai Buccal funnel with numerous teeth which radiate from the 

 mouth in all directions (Fig. 10). 

 bi Dorsal fin continuous; GreatLakes and Mississippi Valley. . i. I chthyomyzon, 



b2 Two separated dorsal fins; Atlantic slope 2. Petromyzon. 



a2 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) 3- Entospkenus. 



bo No such row of teeth present (Fig. 13) 4- Lampetra. 



I. 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: 2 species. 



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

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



