LAMPREYS AND HAGS 



61 



the pharynx ; this, with other related conditions, has caused 

 Myxine and Bdellostoma to be included in a sub-group 

 of Cyclostomes, as Myxinoids, or Hyperotretes* In each 

 genus there is possibly no more than a single valid species. 

 Myxine is a well-known form : it occurs along the Atlan- 

 tic coast at moderate depths. It is exclusively carnivorous, 



Fig. 12. A-D. Ventral aspects of heads of (A) 

 Bdellostoma (after AYERS) ; (B) Myxine (after GCJN- 

 THER) ; (C) Ammoccetes (after GiJNTHER) ; (D) Pe- 

 tromyzon (after GUNTHER). 



often boring its way into the abdominal 

 cavity of (diseased or injured) fishes, and 

 with them is brought to market; it is 

 also taken not infrequently by line fisher- 

 men. The smallest example that has 

 thus far been described is 6 cm. in length ; it was 

 recorded by Beard. (V. Ref. p. 239). 



The Lamprey, Petromyzon, is the most perfectly studied 

 member of the Cyclostomes. Its species are common 

 to the continents of the northern hemisphere ; and in 

 South America and Australia there occur very closely 

 allied genera, as Mordacia and Geotria. The largest 

 lamprey, P. marinus (Fig. 72, and C, D\ is known to 

 attain a length of nearly four feet ; it occurs in the coast 



* v. Glossary, p. 228. 



