CESTEACIONTIDJE. 
By C. W. De VIS, M.A. 
A small tricuspidate tooth (plate ii, fig. 3), observed by Mr. Berney 
on the weathered edge of a mass of molluscan remains, affords the 
following means of discrimination :— Median cusp broad and low, 
its height about equal to its breadth at the base, edges convex, 
point obtuse, base cleft, a channel ascending from cleft merging 
into an impressed area which occupies much of the surface of the 
crown, crown smooth (except for the angular edges of the impression), 
and towards the base tumid on each side of the impression ; right 
lateral cusp high, nearly as high as the median, narrow, subulate ; 
left lateral cusp small, smooth, similar to the median in form ; left 
limb of root prolonged, right possibly so. 
These characters approach so nearly to those of the prehensile 
teeth of certain species of Ryhodus that one need have little hesita- 
tion in concluding that the tooth under view represents a member 
of that genus. Whence it appears that our Port Jackson shark 
was not without an ancestor in our cretaceous sea. To this tooth 
may be allotted the name Ryhodus incussidens. 
