I'ETllOMYZONTTD.i:. 499 



Subclass V. CYCLOSTOMATA. 



Skeleton cartilaginous and notocliordal, without 

 ribs, and without real jaws. Skull not separate from 

 the vertebral column. No limbs. Gills in the form 

 of fixed sacs, without branchial arches, six or seven in 

 number on each side. One nasal aperture only. 

 Heart without bulbus arteriosus. Mouth anterior, 

 surrounded by a circular or subcircular lip, suctorial. 

 Alimentary canal straight, simple, without coecal ap- 

 pendages, pancreas, or spleen. Generative outlet pe- 

 ritoneal. Vertical fins rayed. 



Cfr. MiiUcr, Abhandl. Ak. Wiss. Berlin, 1834, p. 7G.— These fishes 

 were named MarsipohruncJui by Bonaparte, and form one of the 

 two suborders of the Subclass Dermopteri of Owen (Auat. Vert. i. 

 p. 7). Midler has divided them into two families : — 



I. PetromyzontidsB. The uasal duct terminates blind, not pene- 

 trating the palate (p. 499). 



II. Myzinidae. The nasal duct penetrates the palate (p. 510). 



Fam. 1. PETROMYZONTIDiE. 



Cyclostomata hyperoartia, MMer, AhhnniU. Ak. Wiss. Btrl. 1&34, 

 p. 77. 



Body eel-shaped, naked. Subject to a metamor- 

 phosis. In the perfect stage with a suctorial mouth 

 armed with teeth simple or multicuspid, horny, sitting 

 on a soft papilla. Maxillary, nKuuUbulary, lingual, 

 and suctorial teeth may be distinguished. Eyes pre- 

 sent (in mature animals). External nasal aperture in 



2 K 2 



