PLATYSTERNID. 45 
Fam. 5. PLATYSTERNIDZ. 
Elodites Cryptodéres, part., Duméril § Bibron, Erp. Gén. ii. 1855, 
Emydide, part., Gray, Cat. Tort. 1844, and Sh. Rept. i, 1855. 
Chersemyda, part., Strauch, Chelon. Stud, 1862. 
Platysternide, Gray, Suppl. Cat. Sh. Rept. i. 1870. 
Nuchal plate without costiform processes. Plastral bones nine. 
Shell covered with epidermal shields. Caudal vertebrae mostly 
opisthoceelous. Neck completely retractile within the shell. Tem- 
poral region completely roofed over; no parieto-squamosal arch. 
Digits moderately elongate ; phalanges with condyles; claws four 
or five. 
1. PLATYSTERNUM. 
Platysternon, Gray, Proc. Zool. Soe. 183 1, p. 106; Dum. § Bibr. 
p- 848 (1835); Gray, Cat. Tort. p. ¢ 35 (1844), and Sh. Rept. 1. p. 19 
£1855) Strauch, Chelon. Stud. p. 54 (1862); Giinth. Rept. Brit. 
Ind. p. 42 (1864) ; Gray, Suppl. Cat. Sh Rept, i, p. 69 (1870). 
Plastron moderately large, connected with the carapace by liga- 
ment; a series of inframarginal shields separates the plastral shields 
from the marginals, Head very large, covered above with an un- 
divided horny shield; jaws very strong, hooked, without additional 
alveolar ridges. Digits feebly webbed, all except the outer toe 
clawed. ‘Tail very long, subcylindrical, compressed at the end, with 
rings of squarish shields. 
S. China, Siam, Burma. 
The affinities of the freshwater Tortoise which is the only known 
representative of this family are to a nearly equal degree with the 
Testudinidee and with the Chelydride. The similarity of the skulls 
of Platysternum and Macreclemmys is very striking ; but in the 
former the temporal roof is still more developed without, however, 
attaining the stage of the marine Turtles, in which the parietal 
bones join the squamosals; and the jugal presents this peculiarity, 
unique among Chelonians, that it is completely enclosed between 
three bones, viz. the postfrontal, the maxillary, and the quadrato- 
jugal. The cervical vertebra are as in a typical Emydoid ; second 
and third opisthoceelous, fourth and eighth amphicyrtous, fifth and 
sixth proccelous, seventh amphiccelous; there are three ginglymoid 
articulations (v., vi., vil.). The symphysial branches of the pubis 
and ischium are parallel, but connected only by ligament. The 
three anterior caudal vertebrae are proccelous, the next amphiccelous, 
then fellow a series of nineteen opisthocelous ; the last ten are 
again procelous. ‘The neural plates form a complete series; they 
are, with the exception of the first, broader than long and hexa- 
gonal, Two pygals are present, in addition to the azygos marginal, 
The plastron is separated from the carapace by ligament, and 
