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 tind conehiding 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 Enalosauri, 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- 
spicuons character of this genus consists in the cervical vertebre, 
which are considerably shorter than those of the dorsal region: 
- in this respect it differs from all recent Saurians, the vertebra 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 
