268 THE GALAPAGOS TORTOISES. 
season, there may be a thick and strong covering that is increased in thickness 
by successive growths in its duration. The earliest slough in some marine 
tortoises is well described in Fry’s remarks on Chelonia depressa in, 1913, 
Records of the Australian Museum, 10, p. 162, ‘‘Chelonia depressa then, emerges 
from the egg with each scute covered by a ‘larval shield’ which, as the animal 
grows, becomes an areola almost identical with that found in land tortoises; 
this is finally shed before the turtle reaches maturity, leaving the smooth scutes 
described by Garman and figured on Pl. XXI-X XII. As far as I can ascer- 
tain these areolae are unique amongst Marine turtles.” Giimther, 1877, dis- 
cussing the land tortoises of the Galapagos, says, p. 18, as long as the Tortoises 
are young, growth, as far as it is externally visible, proceeds along the margins 
of all the scutes; the sutures get broader, appearing as whitish seams, soft and 
very sensitive. After some time the young portion of the epidermis becomes 
horny, and is raised in a line (stria) running along each side of the suture. Ata 
later period this increment takes place only (at least only conspicuously) in 
certain portions of the carapace.’’ Marine and all land tortoises are hatched 
with the larval shield on each scute; it forms the areolar space on the scute 
which in the land species may or may not be shed, but which appears to be 
shed in marine forms at an early date. If not shed all the concentric striae 
remain, unless possibly affected by wear, each successive stria being the index 
to the amount of surface enlargement or growth, beyond the stria immediately 
preceding it. If there were no lateral growth, from starvation or disease, the 
scute, if there were no slough, might thicken by successive accretions beneath 
but possibly might not increase the number of concentric striae around its 
edges. Some specimens from dry localities, have retained the larval shield 
and have never sloughed; year after year they have increased by one or more 
the record of the striae on the scute. Other specimens appear to have kept 
the sloughs and striae for long periods then suddenly by a slough have lost 
the entire record of the series at once and from the striate and grooved condi- 
tion have become smooth and polished, to begin at the edges of each scute 
another striated record, see Plate 27. Testudo clivosa, Plate 21, a twenty-five 
inch specimen may have an entire record. On the youngest specimens, a year 
or more of age, of most if not all of the species in the collection, no slough has 
occurred. The larval shield and all of the striae are in place. Larger speci- 
mens of some of the same species show plainly that through a slough the larval 
shield and the striae have been carried away leaving the carapace smooth; 
still larger ones testify to more or less regularity in sloughing and to consequent 
