24 



Trachodon — Squamata. 



Table-case, 

 No. 16. 



In the genus TracJiodon, of Leidy, all the dorsal vertebrjB 

 are opisthocoeloiis (hollow behind), with low arches, on which 

 the rib-facet rises to the summit of the neural platform ; the 

 centra are moderately compressed and wedge-shaped, with a 

 haemal carina. The teeth are simplei- than in Iguanodon, with 

 lozenge-shaped crowns, the inferior surface of the root of each 

 tooth being grooved for the reception of the summit of the 

 tooth below. In T. cantahrigiensis the crowns of the teeth are 

 relatively broader than in T. Foulki, from New Jersey (see 

 Figures 28, A, B, c) . 



The following are of uncertain affinities, namely: — Echinodon, 

 which was a large saurian probably of aquatic habits. The teeth 

 were flat, broadly pointed, and the upper edges strongly serrated, 

 hence the name "prickly-tooth." A more formidable saurian 



Nuthetes. 



Fig. 23. — (a) lateral, and (n) profile views of a tooth of Trachoilmi cantdbrifiansU 

 (I.ydekker), Greensand, Cambridge; (c), tooth of Trachodon Foulici (Leidy), Upper 

 Cretaceous ofNew Jersey, U.S.A. 



from the same deposit is the Nuthetes destrtictor. The teeth are 

 flat, recurved, and finely serrated on their anterior and posterior 

 margins, like miniature teeth of Megalosanriis which they 

 resemble. 



Order IV.— SQUAMATA (Scale-covered Reptiles). 



This order is largely represented by forms living at the 

 present day, as it includes the true Lizards, the Chameleons, 

 and the Serpents, and in the Cretaceous epoch by the great 

 extinct Mosasaurians. In this order the body may be either 

 short, with well developed limbs and a distinct tail, as in the 

 Lizards ; or it may be extremely elongated without any external 

 trace of limbs, and passing gradually into the tail, as in the 

 Snakes. As a rule, the whole body and limbs are covered with, 

 overlapping hoi-ny scales, and these may be underlain by an 



