THE PHARYNGEAL TEETH OF FISHES. 185 



TTyperopisns hehe, also a Nilotic fish, has thirteen minute 

 gill-rakers on the first epibranchial. There are no gill-rakers 

 on the cerato-hypobranchial of the first arch, nor on the other 

 arches. There is a set of granular teeth on the tongue, arranged 

 at the forward end as the seeds of maize on an Indian corn cob; 

 at the hinder portion of the tongue these teeth are arranged in 

 an outer circle with an inner area of mucous membrane. The 

 palate of this fish is covered with a strong bony plate that has 

 rounded teeth studded on it, against which the teeth on the 

 tongue engage. 



Hyodontid^. 



Tlyodon alosoides, a fresh-water fish, the Mooneyes of Canada, 

 has eight short, thick, horny gill-rakers on the first cerato- 

 hypobranchial arch ; these are not teeth-bearing. There are 

 four on the epibranchial. The longest of the gill-rakers is, in 

 length, just under one-third of the depth of the gill-laminse below 

 it. There are short, thick gill-rakers on the inside of the first 

 arch, and the inner and outer sides of the other arches. There 

 are no upper or lower pharyngeal teeth. There is a strong 

 cardiform tooth on each side of the tongue near the tip, with a 

 smaller, similar tooth near the oesophagus, and other teeth 

 buried in mucous membrane along the centre of the tongue ; and 

 on the basibranchials near the tongue a broad, depressed band of 

 asperities. 



Hyodon tergisus has only four gill-rakers on the. cerato- 

 hypo- portion of the first branchial arch, similar to those described 

 for the last fish. All the other remarks made as to pharyngeal 

 teeth and teeth on the tongue apply equally to this fish. 



OsTEOGLOSSIDiE. 



Osteoglossum bicirrhosum, the "Aroowana" of British Guiana, 

 has twelve long, horny gill-rakers on the cerato-hypo- of the first 

 branchial arch, with ten on the first epibranchial. The longest 

 of the gill-rakers, the second to the sixth from the angle, are 

 about twice the length of the gill-laminse below them ; for the 

 size of the fish it has very short gill-laminse. The inside and 

 outside of the other arches, as also the outside of the fifth arch, 

 all bear gill-rakers shorter than those of the first arch, and 



