60 REPORT—1845. > 
On the Occurrence of the Mosasaurus in the Essex Chalk, and on the Discovery 
of Flint within the Pulp-cavities of its Teeth. By Epwarp Cuarteswortu, 
F.G.S. ; 
This communication relates to the Saurian teeth figured in the ‘ Odontography’ of 
Professor Owen under the generic name Leiodon, and to a fragment of a jaw of this 
reptile in Mr. Charlesworth’s possession from one of the chalk quarries on the banks 
of the Thames. Mr. Charlesworth contends that there are no grounds to warrant 
the establishment of the genus Leiodon. He refers the teeth described under that 
name to the genus Mosasaurus, and proposes the specific name stenodon (narrow- 
toothed) to distinguish the English fossil from its congener, the Mosasaurus Hoffmanni. 
A section of the jaw made at right angles to its long axis, and through one of the 
conical bases upon which the teeth are implanted, exposed a piece of black flint, 
filling the extension of the pulp-cavity into the substance of the jaw. Two more of 
the pulp-cavities, upon being laid open, exhibited the same phenomenon; in one 
case the flint filling the entire cavity, so as to occupy the hollow of the tooth itself; 
but no deposit of flinty matter had taken place in the bony material of the jaw. 
Mr. Charlesworth considers that the discovery of flint under these remarkable cir- 
cumstances is strong presumptive evidence in favour of its having been deposited 
from an aqueous solution, and is opposed to the respective theories adyanced by M. 
Ehrenberg and Mr. Bowerbank to explain the formation of flints in chalk. 
Notice of the Jaws of an Ichthyosaurus from the Chalk in the neighbourhood 
ris / 4 of Cambridge. By Mr./Carrer. 
The author supposed these remains would constitute a new species, the teeth 
differing in a very remarkable manner from those of any [chthyosaurus which he had 
been able to examine, or of which he could find published descriptions. ‘The dental 
groove of the lower jaw is placed in a different plane from that of the upper, and 
the apposition of the upper and lower ranges of teeth is effected by the roots of the 
lower teeth developing themselves in a curved direction. Considering it probable 
that this peculiarity is characteristic of the species, he proposes to give it the name 
campylodon, from the Greek word kampulos, ‘ bowed or bent.’ 
Mr. Carter has also discovered teeth and vertebrae of the same species in the 
upper greensand near Cambridge. 
On Posidonian Schist amidst Trappean Beds, and on Traces of Drift-ice in 
the South of the Isle of Man. By the Rev. J. G. Cummine, M.A., of © 
Emmanuel College, Cambridge, and Vice-Principal of King William's Col- 
lege, Isle of Man. 
The steps of St. Paul’s cathedral, presented by the venerable Bishop Thomas 
Wilson, are the produce of certain quarries at Poolvash in the Isle of Man. 
The bed from which they were taken is an impure schistose black limestcne, cha- 
racterized by very fine and perfect Posidonie. 1t is remarkably interposed between 
beds of regularly stratified trap-tuff, and though the order of superposition shows it 
to be of later date than the light-coloured limestone of Poolvash; in mineralogical 
and paleontological character it presents a return to the lowest limestone of this 
basin. 
The first object of this paper is to trace out the condition of this area at the period 
of this deposit ; and the second, to notice some of the more remarkable changes which 
have since passed over it. : 
The elevation at different periods of the schists and other older rocks which con- 
stitute the mountain-chain of the island, running irregularly nearly north-north-east 
and south-south-west from the Calf of Man to Maughold Head, has formed on the 
south-western side around Castletown a semi-elliptical basin, the extremity of the 
major axis being Coshnahawin in the north-east, and Perwick Bay near Port le 
Murray in the south-west. These schists seem to be lower Silurian, but, containing — 
only a few fucoids (as far as seen hitherto), their exact age is uncertain. q 
Resting unconformably upon them, we have the old red conglomerate, which is — 
