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 ' 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. "\Ye add here a list of the species of Ptychodus ex- 
hibited in our National Collection. 
SPECIES OF PTYCHODUS IN BRITISH MUSEUM COLLECTION. 
Palatal Teeth of 
Ptycliodus X)oly gyrus . . . From "White Chalk, Burham, Kent, Wiltshire, Lewes, 
Sussex, Purfleet, Grays, Essex (Taylor's CoUection). 
Pty. dejiressus "White Chalk of Cherry Hintou, Cambridgeshire. 
Pty., n.sp "VN'hite Chalk (Taylor's Collection). 
Pty. Oweni "VN'hite Chalk, Burham, Lewes. 
Pty. Mortuni Cretaceous strata, Clarke County, Alabama. 
? P^y (specimens caUed nas- U ^^^^ ^.j^^ ^ g^^^^^^ 
cent teeth) J 
Pty., sp. (near polyyyrus) . . L^pper Greensand, Tournay. 
Pty. rugosus "\A'hite Chalk, Rochester, Greenhithe, Kent. 
Pty. altior Chalk, Sussex, 
Pty. decnrrens Lower Chalk, Kent (Taylor's CoUection), Harietsham, 
Burham, Maidstone, Kent, Brighton. 
Pty. mammillaris .... Lower Chalk, Lewes, Brighton, Dover, Guildford ; 
Upper Greensand, Tournay; Chalk Marl, Toplitz. 
Fix Rays of 
Ptychodus spedabilis . . . "White chalk, Lewes. 
Pty., sp, (small size) . . . Chalk, Sussex. 
Pty. arcuutus Chalk, Lewes. 
Pty, cibberulus Chalk, Lewes. 
ty. articulatus Chalk, Lewes. 
Pty., sp "V\'hite 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 StropJio- 
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- 
