86' 
TORTOISES AND TURTLES. 
This is effected by immersing it in hot water, and then allowing it to cool under 
heavy pressure between smooth blocks of wood, or metallic plates. The surface is 
then rendered smooth, and the thickness equal, by scraping and filing away the 
rough and prominent parts. In this way each plate receives an equal and smooth 
surface. But it is in many cases desirable to employ larger pieces than can be 
obtained from single plates, and two pieces are then united together in the 
following manner. The edges are bevelled off’ to the space of two or three lines, 
and the margins, when placed together, overlap each other to that extent. They 
are then pressed together by a metallic press, and the whole is submitted to the 
action of boiling water; and by this means the two pieces are so admirably 
soldered together as to leave no indication of the line of union. By the application 
of heat, also, the tortoise-shell may be made to receive any impression by being 
pressed between metallic moulds.” Necklaces, etc., are made by pressing the 
fragments and dust in moulds. 
Turtles, more or less closely allied to the existing kinds, abound 
in marine strata of the Tertiary and Cretaceous epochs, some belong¬ 
ing to extinct and others to the living genera. Among the latter, the gigantic 
Hoffmann’s turtle (Chelone hojfmanni), from the chalk of Holland, appears 
to have been allied to the hawksbill, but had a shell of some 5 feet in length. 
Extinct loggerheads occur in the London Cl a} 7 ; and an allied extinct genus 
(. Lytoloma ), common to the same formation and the upper Cretaceous deposits, was 
remarkable for the great length of the bony union between the two branches of 
the lower jaw, and also for the circumstance that the aperture of the internal 
nostrils was placed right at the hinder extremity of the palate, as in crocodiles. 
In strata older than the Chalk, such as the Purbeck and other Oolitic rocks, we 
meet with turtles having heart-shaped shells, but clawed limbs, and a vacuity in 
the centre of the plastron, these forming an extinct family ( Acichelyidce ), from 
which the modern turtles have probably originated. 
Extinct Turtles. 
Leathery Turtles. 
Family DERMOCHEL YIDIE. 
The remarkable leathery turtle, or luth (Dermochelys coriacea), which is the 
solitary survivor of a series of extinct forms, is one of those animals whose serial 
position is a matter of dispute among naturalists; some of whom regard it as so 
different from all other Chelonians, that it ought to represent a suborder by itself, 
while others believe it to be merely a highly specialised form allied to the true 
turtles. From the evidence afforded by extinct species, the latter view, to our 
thinking, appears the more likely to be the true one. The essential peculiarity of 
the leathery turtle is to be found in the nature of its carapace, which is a mosaic¬ 
like structure composed of a number of irregular discs of bone closely joined 
together, and entirely free from the backbone and ribs. In certain extinct forms 
the carapace, on the other hand, is represented merely by a row of marginal bones; 
from which it is inferred that these reptiles have been derived from true turtles by 
a gradual disintegration and breaking up of the carapace. In the living genus the 
