No. 384.] CHELONMIAN CARAPACE AND PLASTRON. 943 
neural scutes the lines of growth show that the tubercle at the 
posterior border is the starting point ; and from there the scute 
spreads mostly forward and laterally. In the costal scutes the 
growth begins near the upper hinder angle and spreads down- 
ward and forward. If there is a lateral keel, its tubercles form 
the starting point. From these the scutes have spread toward 
the marginals, and between the former and the latter the supra- 
marginals have been suppressed. It might be supposed that 
the manner in which the epidermal scutes extend themselves 
is determined by the growth of the underlying bones; but a 
study of the relations of the two sets of structures will, I think, 
disprove this idea. These scutes are simply following the course 
laid down by their predecessors. In some of the higher turtles, 
as species of Testudo, the centre of growth, the areola, of some 
of the scutes has moved nearer the centre of the scute. 
The great scutes of the plastron all grow from a point near 
the posterior outer angle forward and toward the mid-line where 
they have met. In doing this they have suppressed the scutes 
of the middle keel. To a less extent they have grown upward 
and forward, and have thereby suppressed partially or wholly 
the inframarginals. 
If the reader will examine the figures on Pls. XXII-XXV, 
of Gray’s Catalogue of Shield Reptiles, Pt. i, and Pl. VI of 
Boulenger’s Catalogue of Chelonians, he will find a large scute 
on the mid-line of the plastron of each of the turtles there 
depicted, near the anterior end, and, except on Pl. XXIII, sur- 
rounded by other scutes. This is the intergular. It occupies 
the position where the median and first pair of lateral keels of 
Dermochelys come together. Indeed, it is located rather on 
the territory where the median keel would end anteriorly. Its 
lines of growth show that it spreads from a central point in all 
directions. This intergular has very much the appearance of 
having originated from the median plastral keel. Usually the 
intergular extends forward to the anterior margin of the plastron 
and is smaller, as in Gray’s Catalogue, Pls. XXVII, XXVIII 
(Podocnemis). In such cases it less forcibly suggests an ori- 
gin from the median keel, and has evidently undergone great 
reduction. 
