328 E. T. NEWTON ON TWO CIIIM^EROID JAWS FROM 



number of tubes (filled with dark substance), generally set perpendicu- 

 larly to the surface, around which the dentinal substance is deposited. 

 A surface-view of a portion of one of these tubular teeth is shown 

 in tig. 3. The tooth b (fig. 1) is small, and placed at the anterior 

 end of the upper margin of the symphysis. The tooth near the let- 

 ter c causes the projection upon the oral margin, and extends inwards 

 almost to the large central one, e. The posterior and outer tooth, 

 d, extends for some little distance near to the margin of the bone. 

 The median tooth, e, is much larger than either of the others ; 

 in this species there is always a space between it and the symphy- 

 sial tooth, b. Below and behind the teeth the bone is covered by a 

 delicate layer of enamel-like substance, which is smooth and shining 

 and shows definite lines of growth. The symphysial surface (sy) 

 is slightly convex ; but towards its oral margin it is marked by a 

 deep groove with a rounded and projecting ridge immediately above it. 



If Agassiz's type specimen (fig. 4) be compared with the more 

 perfect one described above (fig. 1), the close resemblance in every 

 particular will, I think, be obvious, the greatest difference being 

 that the middle tooth (e) is larger in the type (fig. 4) ; this differ- 

 ence, however, must be regarded as of little importance, as it is al- 

 most wholly due to the fact that the bony covering is more broken 

 away in the latter. . 



It might be thought that the differences in general outline and in 

 the form of the teeth between the two specimens represented by figs. 

 1 and 4 would justify their being referred to different species ; but the 

 examination of a large series from the Gault and Cambridge deposits 

 has convinced me that /. brevirostris varies to a far greater extent 

 than is shown in these two specimens. In some instances the tooth 

 e is narrower than it is in fig. ] , and extends almost to the oral 

 margin at c ; in other cases the same tooth will be proportionally 

 much wider, and placed further back. The extent to which the 

 oral margin is indented also varies much, being sometimes more, 

 and sometimes less than in fig. 1. The proportional length of the 

 oral margin from a to d likewise varies. 



The New-Zealand specimen (fig. 5) has the outer surface imbedded 

 in the matrix, and a portion of the beak broken off; but still the 

 fossil is sufficiently perfect to allow of a very close comparison. 

 The description of the Cambridge mandible given above would 

 answer equally well for this one from the Antipodes ; but a 

 comparison of the two (figs. 1 & 5) will show that there are some 

 differences. When, however, the variations which are known to 

 occur among the Gault specimens belonging to this species are duly 

 considered, these differences will be regarded as of minor impor- 

 tance. The greatest dissimilarities are these : in the New-Zealand 

 specimen the oral margin was probably shorter and less indented, 

 the margin from d to x is proportionally longer, and the middle 

 tooth e is larger, and extends further forward and nearer to the 

 symphysial tooth, b. If now the figs. 1, 4, & 5 be compared, it 

 will, I think, be acknowledged that there is as great a difference 

 between the Cambridge and the Folkestone specimens (figs. 1 & 4) 



