230 Transactions. — Zoology. 



skull, with its two bars and additional bones, the pharyngeal cavity is 

 enormously enlarged. When the tuatara inspires it greatly depresses the 

 hyoid and trachea, thereby still more enlarging the pharyngeal cavity. By 

 this means the tuatara inhales a large quantity of air, filling the lungs, 

 mouth, trachea, and the large pharyngeal cavity. This peculiar mode of 

 respiring by depressing the hyoid bone (which with its cornea is very 

 large) enables the tuatara to inhale sufficient air to allow it to remain under 

 water for hours without coming to the surface to breathe. The quantity of 

 air in the lungs, trachea, mouth, and distended pharynx amounts to several 

 cubic inches, which is sufficient to sustain life for some time in a small and 

 cold-blooded reptile. 



Tuataras swim freely — sometimes with only the nostrils above water, at 

 others swimming as freely and well under it. As tuataras are found usually 

 on isles, or on the banks of rivers, it may be that they find part of their 

 food in the water. The Ichthyosaurus and Plesiosaurus marine rej)tiha had 

 abdominal ribs, and the former amphicoelian vertebrae like the Sphenoclon. 

 Dissection of Female Tuataras. 



Total length, 16 inches, of which 8| inches were tail. Dorsal spines 

 beginning at the occiput stretch along the back to the end of the tail ; 

 between the scapulaa five or sis are wanting, and about three over the 

 sacrum. Those on the neck and trunk are flattened laterally, blade-like, 

 and acuminated ; they are quite soft, and many are not erect. The caudal 

 spines are attached one to each section of the verticellated tail. About the 

 middle of the tail, instead of being flattened laterally they are prismoidal, 

 being much wider at the base and not so sharp. As the tail sections 

 dwindle so also do the spines till they can scarcely be said to exist. This 

 tuatara has ten cervical spines, then an interval between the shoulders, 

 then fifteen dorsal, an interval over the sacrum, and forty-one caudal spines. 

 In Lophocalotes interruptus the spines, as in Sphenoclon, reach from the head 

 to end of tail, and are also interrupted between the scapula and over the 

 sacrum. So also in Tiaris tuherculata; in this lizard there is on each side a 

 row of secondary spines. In Sphenoclon, as in certain other lizards where 

 the spines are absent between the scapulae, their place is occupied by a large 

 black patch of skin ; some spines are also black. The skin of Sj^henodon is 

 maxked by several ridges which reach from head to tail, running parallel 

 with the dorsal crest. One ridge extends along the trunk from the fore to 

 the hind limbs ; it is due to the free projecting ends of the abdominal ribs. 



Two ridges beginning at the end of the rounded snout run backwards 

 above the nasal openings and the eyes, giving a triangular look and a flat 

 appearance to the form of the head. In many places the epithelial cells are 

 accumulated, forming small spines which h'regularly croAvn some of these 

 skin ridges. 



