Fishes of the Western North Atlantic 43 



Myxine (no specific name) Cole, Anat. Anz., 2y, 1905: 323 (anat., good descr. of teeth, specimens recorded 



with 7 gills on one side, or both). 

 Myxine atlantica Regan, Ann. Mag. nat. Hist., (8) 11, 191 3: 398 (class., descr., off Nova Scotia) ; Holly, in 



Schultze, Kukenthal, et al., Tierreich, Lief 59, 1933: 49 (class., descr.). 



Order PETROMYZONIDA 



Description. In the adult, seven pairs of gill pouches open separately to the exterior, 

 but open inwardly into a special respiratory tube which is separate from the pharynx and 

 which ends blind, posteriorly; however, this respiratory tube connects with the mouth 

 anteriorly/' At the time of metamorphosis this tube loses its connection with the intestine, 

 while a new pharynx develops above it to form a forward extension of the intestine which 

 connects with the mouth. Snout without barbels; dorsal and caudal fins separate, supported 

 by rays; nostril a blind sac, on dorsal surface of head, not opening into mouth; mouth 

 opens as a funnel or disc surrounded by a circular lip with numerous horny teeth ; sides 

 of trunk without prominent rows of mucous pores; ear with two semicircular canals; eye 

 well developed, with lens and iris in adult, although rudimentary in larva; cranium par- 

 tially roofed over; notochordal sheath with rudimentary neural arches; a complex cartilag- 

 inous basket around gill pouches; intestine with slight spiral fold, apparently homologous 

 with the spiral valve of the Chondrichthyes; pancreas represented by scattered follicles. 



Development. Sexes separate; eggs small, numerous; development, with larval 

 (Ammocoete) stage, different in appearance structurally from adult. In some of the 

 fresh water species the growth stage that normally occurs between the times of metamor- 

 phosis and sexual maturity is omitted.*' 



Habitat. Fresh water, or entering fresh water to breed if marine. 



Families. The single family Petromyzonidae, in which the various Lampreys have 

 been grouped, has been divided recently into two subfamilies, which, in our opinion, may 

 well be raised to the rank of families as follows:** 

 la. Upper margin of central mouth with only one dental plate; margin of oral funnel 



with a series of fringed, as well as smooth, papillae. Petromyzonidae, p. 43. 



lb. Upper margin of central mouth with two separate dental plates; margin of oral disc 



with only smooth papillae or cirri. Mordaciidae. 



Australia, Tas- 

 mania, Chile. 



Family PETROMYZONIDAE 



Characters. Upper margin of the central mouth with only one dental plate, usually 

 toothed; margin of oral funnel or disc with a series of fringed lappets, as well as a series 

 of smooth marginal papillae. Characters otherwise those of the order. 



42. This respiratory tube represents the pharynx of the larva, into which the gill sacs then open. 

 4.3. For discussion, see Hubbs, Pap. Mich. Acad. Sci., ^ ist half, 192+: 587. 



44. Based on the definitions by Holly (in Schultze, Kukenthal, et al., Tierreich, Lief 59, 1933: 12) and by Piet- 

 schniann (in Kukenthal and Krumbach, Handb. Zool., 6 [i]. Lief 5, 1935: 54°). 



