328 Proceedings of the British Association. 



adherent portions without breaking. The mixture is applied hot, 

 and allowed to harden for twenty four hours, when it will come 

 off without injuring the finest parts. The matrix thus prepared 

 requires a strong varnish to protect the back and sides from the 

 action of the liquid in which it is to be placed, and only one copy 

 can be made from each matrix, but the impressions have none of 

 the defects so apparent in those produced in the ordinary moulds. 

 Different lights and shades may be given to the copper impres- 

 sions, by a galvanic process, which the author considers capable 

 of improvement, and application to other purposes. For a dark 

 object on a light ground, the surface is brushed over with the 

 argento-cyanide of potassium, giving it a silver face, which may 

 be removed to the desired extent from the portions requiring to 

 be dark, by a dilute solution of nitro-muriate of platinum. Other 

 tints may be produced by using a solution of gold ; and all may 

 be considerably varied by changing the time during which each 

 solution is allowed to act. 



^ Prof Owen communicated the second and concluding portion 

 of his Report on British Fossil Reptiles. After some prefatory 

 observations on the general nature and affinities of the recent and 

 extinct reptilia, and the parts of the organization of the latter, 

 which by their modifications afford the best character for their 

 determination, the author proceeded to give a recapitulation of 

 the leading peculiarities of the Enaliosauri, which formed the 

 subject of the first part of his Report : and a brief summary of 

 the results of the labors of previous geologists and anatomists, in 

 the field which the second part of his Report had led him to ex- 

 plore. The first section of the Report was devoted to a descrip- 

 tion of a large reptile, the type of a new genus, to which the 

 name Pliosaurus was given, and which formed the link connect- 

 ing the Plesiosaurus with the crocodile family. The most con- 

 spicuous character of this genus consists in the cervical vertebrge, 

 which are considerably shorter than those of the- dorsal region: 

 in this respect it differs from all recent Saurians, the vertebrae of 

 which are characterized by retaining the same length throughout. 

 From this cause, the neck of the Pliosaurus is short, compared 

 with that of the Plesiosaurus, and approaches the condition of 

 that region in the Ichthyosaurus. The more crocodilian propor- 

 tions of the teeth also distinguish it from the Plesiosaurus, which 

 in other respects it strikingly resembles. Remains of it have 



