1, CIIELYS. 207 



Si/no2)sis of the Genera. 

 ]. Neck longer than the dorsal vertebral column ; jaws weak. 



Nose ending in a tube ; fore limb with five claws, hind limb with 

 four : a broad parieto-squamosal arch ; neural plates present. 



1. Chelys, p. 207. 



Both fore and hind limbs with four claws ; nuchal shield behind the 

 marginals, simulating a sixth vertebral ; a slender paricto-squa- 

 mosalarch; neural plates present .. 2. Hydromedusa, p. 210. 



Both fore and hind limbs with four claws ; intergular shield behind 

 the gulars ; no parieto-squamosal arch ; no neural plates. 



3. Chelodina, p. 213. 



II. Neck shorter than the dorsal vertebral column. 



A. Lower jaw narrow at the symphysis ; first vertebral shield 



larger than second. 



Neural plates present ; parietal bones not expanded superiorly ; 

 parieto-squamosal arch very slender. . 4. Rhinemys, p. 217. 



Neural plates present ; parietal bones expanded superiorly ; parieto- 

 squamosal arch strong 5. Hydraspis, p. 210. 



Neural plates absent; parietal bones much expanded superiorly; 

 vertebral region grooved 6. Platemys, p. 220. 



B. Lower jaw, at the symphysis, at least as broad as the orbit ; 



first vertebral shield not larger than the second. 



Alveolar surface of upper jaw without median ridge. 



7. Emydura, p. 228. 



Alveolar surface of upper jaw with a median ridge. 



8. Elseya, p. 234. 



1. CHELYS. 



p. 44 (1844), and Sh. Rept. i. p. 60 (1855) ; Strauch, Chelon. 

 Stud. p. 49 (1SC2); Grai/, Suppl. Cat. Sh. Bept. i. p. 71 (1870). 

 Matamata, Merrem, Tent. p. 21 (1820). 



Neural plates present, seven in number, the last pair of costals 

 forming a suture ; nuchal shield present, marginal ; plastron narrow, 

 with very strong axillary and inguinal buttresses, the latter anchy- 

 losed to the fourth costal plate. Neck longer than the dorsal 

 vertebral column. No separate nasal bones ; a strong siqjraoccipital 



