64< London FAectrical Society. 



reptiles ; and he shows that it is distinct from the Polkilopleuron of 

 M. Deslongchamp by the long bones of that Saurian having medul- 

 lary cavities. 



Saurian Teeth from the Lower Greensand. — These teeth, described 

 by Mr. Owen in his ' Odontography ' under the name of Polypty- 

 chodon, are characterized by the crown presenting numerous closely 

 set longitudinal ridges, which are continued, of nearly equal length, 

 to near the apex of the crown. In their size and simple conical form 

 the teeth of the Polyptychodon resemble those of the great sauroid 

 fish, Hypsodon, Ag., but may be distinguished by the solid compact 

 structure of the dentine, which is resolved by decomposition into 

 successive cones ; and also by the ridges on the exterior of the crown 

 of the Hypsodon' s teeth being alternately long and short, and ter- 

 minating abruptly at different distances from the base, the interspaces 

 between the longer ridges widening as they approach the apex. The 

 tooth of the Polyptychodon is slightly and regularly curved, and in- 

 vested with a layer of enamel of a clear, amber-brown colour, and of 

 ■which the ridges are composed, the surface of the outermost layer 

 of dentine being smooth. A tooth from the lower greensand near 

 Maidstone has a crown three inches long, and one inch four lines 

 across the base. It consists of a body of compact dentine composed 

 of successive lamelliform cones, and has a short and wide conical 

 cavity at the base. 



From the teeth supposed to have belonged to the Polkilopleuron, 

 the specimens above described differ in the ridges on the crown 

 being greater in number and more closely set, as well as in the form 

 of the teeth being nearly circular instead of elliptical ; from the teeth 

 of the Pliosaurus they differ also in being round and not three-sided, 

 and in having longitudinal ridges over the whole surface of the crown ; 

 and from the teeth of the Mosasaurus they differ in being ridged 

 and not smooth. 



In conclusion, Mr. Owen states, that as the Hythe Saurian is di- 

 stinct from all other described Saurians, and as these teeth belonged 

 to a great Saurian also undescribed, and further, as the Maidstone 

 tooth was found in the same formation as the Hythe fossil, so it may 

 be convenient to consider all these remains for the present to have 

 belonged to the genus Polyptychodon, originally proposed for the 

 animal which was provided with the teeth. 



LONDON ELECTRICAL SOCIETY, 

 [Continued from vol. xix. p. 405.] 



Nov. 16, 1841. — The Society met in the Council room of the 

 Adelaide Gallery. The papers before them were, — 1st, " An Experi- 

 mental Inquiry into the Nature of Ozone." By Mr. J. W. Gann. 



The first experiments were made by breaking and making contact 

 between various electrodes (from a series of ten Grove's) in a jar of 

 atmospheric air. Copper, iron, silver, and platinum anodes deve- 

 loped the odour ; zinc did not ; neither did plumbago nor carbon : 

 the same results occurred when the experiments were varied by 

 using oxygen, nitrogen, hydrogen, carbonic acid, and nitrous oxide. 



