Structure of the Fossil Saurians. 341 



senible the teeth of the Mosasaurus, which, however, are 

 placed in actual alveoli. I conceive that I have established in 

 this Phytosaurus, that the fangs of the teeth were free, and 

 stood in a channel in the jaw, and were attached to it in the 

 strongest manner. On the inner side, the row of teeth was 

 probably first surrounded by a lamella, and then by the bone 

 of the jaw. On the outer side, the jaw-bone only appears to 

 have been recognised : nothing of a lamella has yet been dis- 

 covered. In some places, it is not to be disputed, that the 

 change of teeth was effected as in the Crocodiles; that is, in- 

 side of the existing teeth, and growing up from the basis to 

 the points. The names of cylindricodon and cubicodon are 

 derived by Dr. Jaeger from the cylindrical and cubical form of 

 those parts which I consider to be the remains of the teeth. 

 The Ph. cylindricodon had not less than 30 teeth in one half 

 of the jaw ; and yet its beak appears to have been shorter 

 than that of the Gavial. Of the Ph. cubicodon, some con- 

 nected portions of teeth are all that have been found. 



Sauroce'phalus * Harlan. 

 Harlan describes remains of a fossil Saurian under the 

 name of the Saurocephalus lanciformis, of which portions of 

 the jaw only have yet been found ; these, Lewis and Clarke, 

 in their journey to the Missouri, discovered, and presented to 

 the Philosophical Society of Philadelphia, in the museum of 

 which they are preserved. The place of their discovery is a 

 cave, some miles south of Soldier's River Bay : they were, 

 however, undoubtedly, originally deposited in a marine bed of 

 stone at this locality. Judging from those portions of the 

 jaw, the animal must have been 6 "or 8 feet long. The longest 

 teeth measure seven tenths of an inch, of which two tenths 

 protrude above the jaw ; and this portion is covered with 

 enamel, smooth, polished, lancet-formed, and provided with 

 very sharp edges.f The bodies of the teeth are all hollow, 

 and stand in a long channel, not in separate alveoli, but close 

 to each other. Through the body of the bone proceeds a 

 canal for the lower maxillary nerve, in the place of which is 

 perceived a channel along the whole of the teeth under the 

 alveolar portion. The bottom of this channel is penetrated 

 by as many holes as there are teeth, through which the nerves 



* Jaws and teeth of this kind occur in the chalk of Sussex, and are 

 figured in Mantell's Fossils of the South Downs, tab. xxxiii. figs. 7. 9. M. 

 Agassiz has shown that they belonged to fishes : he retains the name 

 Saurocephalus, for the genus. — Ed. 



-j- These remind us of the teeth of a fragment of the jaw which 

 Buckland (dot. Tram., ii. iii. t. 27. f. 3.) attributes to the Pteroclactylus ; 

 which, however, certainly belonged to another animal. 



