//. TYPES IN DETAIL U^TH THEIR SUBORDINATE GROUPS. 39 



T\TE^^^. VERTEBRATA, 



Division I. CYCLOSTOilATA . . Vertebrates with a cirailar sucto- 

 rial moath armed with chitinoas 

 teeth; no jaws; 6-7 pairs of circu- 

 lar gill-openings, 



Gass. MAESrPOBEAHCHn. The only class included here, 



with characteristics of the Division. 

 Its two sub-divisions have the 

 value of Families, as follows : 



FamUy i. Petromyzontida Xasal cavity a median blind-sack. 



(Lamprev eels. ) Mouth without tentacles. They 



attach themselves by their circular 

 mouth to the sides of fishes and 

 suck their blood. Fresh-water 

 and marine forms. 



X Petromyzon. 



Family 2. MyxinidtB. Xasal sack provided with an inner 



(Hag-fish.) palatal opening. Mouth with 



tentacles. Habits more parasitic 

 than the former. Thev push their 

 way even into the body-cavity of 

 other fish and consume their vis- 

 cera. All marine. x Myxine. 



Division H. GNATHOSTOMAT.\.. Vertebrates with mouth in the 



form of a transverse cleft, sup- 

 ported by two jaws; teeth usually 

 present, composed of enamel and 

 dentine. 



A. AXAMXL\ Embryo without amnion or other 



foetal membranes; some have 

 lungs, but all breathe by gills 

 during at least a portion of their 

 life; cold-blooded. 



Super-class L ICHTHYOPSIDA. .A group equivalent in extent to 



Ananmia q. v. 



