Manchestef Jleinoirs, Vol. Ivii. (1912), No. I. 5 



border. Each of these teeth has associated with it a 

 shallow pit from which a tooth has been shed, and in 

 which a replacing tooth will be formed. In some cases 

 both teeth are present at once, a condition which was 

 undoubtedly only transitory ; this curious type of tooth 

 change is very characteristic of the Stegocephalia, and is 

 unknown elsewhere except in the *Crossopter}-gian fish, 

 where it occurs in a very typical form in the vomerine 

 tusks o{ Megalichthys, and no doubt in many other genera, 

 and in Lcpidosteiis. This occurrence seems to me a strong 

 additional reason for regarding the Tetrapoda as derived 

 from this group of fish. 



The outer edge of the palatine has a long bearing 

 with the maxilla, and the anterior end of the bone narrows 

 and has a smooth edge forming the back of the posterior 

 naris. 



The pre-vomcr is a large bone which meets its fellow 

 in a long median suture, behind which it has a long 

 articulation with the pterygoid, which extends backwards 

 until it meets the palatine. These two bones are in con- 

 tact until the posterior naris is reached, when they separate, 

 the pre-vomer forming its anterior border. The lateral 

 edge of the bone articulates with the premaxilla and 

 maxilla, and in front it forms the back of the large 

 anterior palatine vacuity. The pre-vomer carries one 

 large tooth and the pit for its successor. 



The Premaxilla has a very narrow palatal exposure, 

 being solely represented by its tooth-bearing edge, which 

 widens at the middle line into a short, blunt, backward ly 

 directed process. 



The Maxilla is entirely formed by a plate on the side 



* Througliout tliis paper '" Crossopterygian" is used as including only 

 the three families Holoptychiida, Rhizodontida and Osieolepidic of .S. Wood- 

 ward's sub-order Rhipidistia, and excluding Tarrasius, Ca'lacaiithiis and 

 Pol)fteri(s, 



