EOCENE GHELGNIANS EEOM THE SALT-RANGE. 
61 
Sub-order Pleurodira. 
Characters.- — The sub-order is characterised 1 by having the carapace and 
plastron fully ossified and united together ; by the anchy- 
losis of the pelvis to both plastron and carapace ; by the 
absence of at least some of the vertebral bones ; 2 and by 
the presence of only a single heart-shaped supra-pygal 
bone above the pygal, as is shown in the accompanying 
woodcut. Other characters are found in respect of the 
head and neck, which need not be mentioned on this 
occasion. When homy epidermal shields are present, an 
intergular shield is developed on the plastron ; and a 
mesoplastral bone may be present. As additional characters 
of at least many genera, it may be observed that the nuchal 
bone (in the Chelydidce) is smaller than the first vertebral 
shield, and that the suture between the pygal and supra- 
pygal bones is situated above the suture separating the 
pygal shields from the last vertebral shield (as is shown in 
the wood-cut) ; the reverse of these features obtaining very 
generally in the Cryptodira . 3 The sub-order may be 
divided into two families according to the presence or 
absence of horny shields on the shell. from Madagascar. 
Family Carettochelydid^e. 
History . — This family was founded by Mr. Boulenger 4 on Carettochelys 
insculptus, Ramsay , 5 from the Ely River, New Guinea. 
Characters.— The distinctive feature of the family is the absence of epidermal 
horny shields on both the carapace and plastron. 
In Carettochelys the limbs are paddle-shaped, the anterior being much elongated; 
only the first and second digits are furnished with claws ; the plastron is apparentlv 
composed of only the normal nine elements, the mesoplastron (intraplastron) being 
absent ; the vertebral bones are of very small size, and are separated from one another 
by the meeting of the costals in the middle line, and the nuchal bone is greatly 
expanded laterally. 
Genus Hemichelys, nobis . 6 
Characters. — Vertebral bones in contact, and not separated by the costals ; a 
small mesoplastron apparently present. 
1 See Riitimeyer : 5 Verh. Nat. Ges. Basel,’ Vol. VI, Art. 1, pp. 21—33 (1878). 
2 The hinder vertebral bones are absent among the Cryptodira in Cinosternum and Dermatemys. 
Compare the figures in pis. XXI and XXIII of the preceding volume of this work. 
4 Ann. Mag. Nat. Hist. 1887, pp. 170—172. 
5 Proc. Linn. Soc., New South Wales, Vol. I, p. 158, pis. Ill— VI (1886). 
6 Rec. Geol. Surv. Ind., Vol. XX, p. 66 (1887). 
