394 MONOGRAPH OF THE AUSTRALIAN MARSIPOBRANCHIl, 



So far, however, no Hyperotrete can be satisfactorily recorded 

 as having occurred within our limits, but Ileptatrema cirrata, 

 beino- an inhabitant of the New Zealand seas, may occur or be 

 represented by an allied form on our coast.* 



The following synopsis will serve to show the most obvious 

 characteristic of the three genera. 



Eleven or more l^ranchial apertures on each side; the base of the 

 tongue situated between the seventh and eighth pair of 

 branchife 



POLISTOTREMA. 



Six or seven branchial apertures on each side; the base of the 

 tongue situated between the anterior pair of branchiae 



Heptatre.ma. 

 A single branchial aperture on each side 



Myxine. 

 In all pi"obability each genus is represented by a single ^alid 

 species only; sexually they are hermaphrodite, but the ova and 

 sperm attain maturity in each individual at a different period, the 

 ripening of the latter taking place earlier in life than that of 

 the former. 



Order HYPEROARTII. 



The Lampreys. 



Body anguilliform, naked, compressed or subcylindrical in front,, 

 compressed behind; mouth subcircular or oval, suctorial; lips, 

 present, usually fringed, but without barbels; nostril at the upper 

 surface of the head, the nasal duct a blind sac, not penetrating 

 the palate. Eyes present, small. Branchial aj^ertures seven on 

 each side, situated behind the head, the inner branchial ducts 

 terminating in a common tube. Teeth cuticular, horny, simple or 

 multicuspid, resting on soft papillai, those immediately above and 

 immediately below the opening of the oesophagus more or 



* Krefft indeed (Australian Vertebrata, p. 779) gives, under the heading 

 of BiMlodoma cirrhalum, the locality " New Zealand and Australian 

 Rivers " ; but this is obviously a mistake and refers ti) one of the Lampreys.. 



