162 



THE GEOLOGIST. 



good work in this direction being done. By a glance at the British 

 Museum specimens, and a careful looking over of the descriptions and 

 figures in the 1 Poissons Fossiles ' and the ' Geology of Sussex,' any 

 intelligent observer would at once see what new additions would be 

 useful for supplying the missing links in the historic and stratigra- 

 phical series. We add here a list of the species of Ptychodus ex- 

 hibited in our National Collection. 



SPECIES OF PTYCHODUS IX BRITISH MUSEUM COLLECTION. 

 Palatal Telth of 



Ptychodus polygyrus . . . From White Chalk, Burham, Kent, "Wiltshire, Lewes, 



Sussex, Purfleet, Grays, Essex (Taylor's Collection;. 



Pty. depressus White Chalk of Cherry Hinton, Cambridgeshire. 



Pty., n.sp White Chalk (Taylor's Collection). 



Pty. Oweid White Chalk, Burham, Lewes. 



Pty. Mortoni Cretaceous strata, Clarke County, Alabama. 



? Pty (specimens called nas- \ Lower Chalk, Dover, Sussex. 



cent teeth) J 



Pty., sjj. (near polygyrus) . . Upper Greensand, Tom-nay. 



Pty. rugosus White Chalk, Rochester, Greenhithe, Kent. 



Pty. altior Chalk, Sussex, 



Pty. decurrens Lower Chalk, Kent (Taylor's Collection), Harietsham, 



Burham, Maidstone, Kent, Brighton. 



Pty. mammillaris .... Lower Chalk, Lewes, Brighton, Dover, Guildford ; 



Upper Greensand, Tournay ; Chalk Marl, Toplitz. 



Fin Rays of 



Ptychodus spectabilis . . . White chalk, Lewes. 



Pty., sp, (small size) . . . Chalk, Sussex. 



Pty. arcuatus Chalk, Lewes. 



Pty. ciblerulus Chalk, Lewes. 



ty. articulatus Chalk, Lewes. 



Pty., sp White Chalk, Burham. 



Pty. latissimus White Chalk, Herts, Lewes, Kent, Southeram; Creta- 

 ceous deposit ? at Oxford, Essex. 



Pty. paucisulcatus .... Chalk, Sussex. 



In the same cases with the Ptychodus teeth is a tooth of Stroplw- 

 dus asper — the type specimen figured by Agassiz. There are also 

 some other specimens and fragments of Strophodus, to which genus I 

 am disposed to add the specimens and fragments labelled " nascent 

 teeth of Ptychodus," and so styled in Dixon's work by Sir Philip 

 Egerton. A comparison of the structure of one specimen in parti- 

 cular, with one of the specimens of S. magnus from the Stonesfield 

 Slate of Eyeford, in the adjoining case will, we think, justify this view. 

 "Without wishing to do more than hint the possibility that the an- 



