404 CHELONIA CHAP. 



aestivation in the summer. The last winter they spent buried 

 in the moss, but occasionally, especially on bright and sunny 

 days, they went into the water for a few hours, chiefly to drink, 

 but sometimes also to take a little food. 



Hydromedusa, a South American genus, has a neck even longer 

 than that of Chelodina, which it much resembles externally. But 

 the nuchal shield, large and broad transversely, is situated behind 

 the anterior marginals, looking therefore like a sixth neural 

 shield. The neural plates form a continuous row, only the last 

 pair of costal plates meeting in the middle line. H. tectifera 

 occurs in Southern Brazil, and in the La Plata. The shell is 

 dark brown above ; yellowish, with dark spots, below ; the head 

 and neck are olive-coloured, adorned with a broad white, black- 

 edged band on either side. Fore- and hind-limbs broadly webbed, 

 and with four claws. Total length of the shell about eight 

 inches. 



Fam. 3. Carettochelydidae. The shell is covered with soft 

 skin instead of horny shields. The limbs are transformed into 

 paddles, with elongated digits, and have only two claws. The neck 

 is short, and not retractile. In other respects the skeleton, not- 

 ably the plastron, pelvis, and skull, conform with the Pleurodirous 

 type. Only one species, Carettoclielys insculpta, still imperfectly 

 known, from the Fly Eiver, New Guinea. Length of the shell 

 of the only complete specimen about 18 inches. This peculiar 

 creature seems to stand in the same relation to the typical 

 Pleurodira, as do the Chelonidae to the Testudinidae, except- for 

 the complete reduction of the horny shields upon the shell, recall- 

 ing in this respect Spliargis and Trionyx. 



Sub-Order 3. Trionychoidea. The shell is very flat, oval, 

 or almost round, and is covered with soft, leathery skin instead 

 of with horny shields. The limbs are broadly webbed, and only 

 the three inner digits are provided with claws. Carnivorous, 

 found in the rivers of Asia, Africa, and North America. 



The head and neck are completely retractile, bending by a 

 sigmoid curve in a vertical plane like that of the Cryptodira. 

 The jaws are concealed by soft, lip-like flaps, and the nose forms a 

 soft short proboscis. The ear is hidden. The skull, Fig. 91, is 

 flat, with three long posterior processes, formed by the supra- 

 occipital above, and the squamosals on either side. The whole 

 temporal region forms a wide, shallow fossa, without any indica- 



