SAUKOPTERYGIA. 239 



teeth for a like purpose are afforded by the class of fishes, as, 

 e. g., by the extinct Pycnodonts, and by the existing wolf-fish 

 (AnarrhicJias lupus) and Cestracion. But the reptilian class 

 is not without its instances at the present day of teeth 

 shaped like paving-stones, of which certain Australian 

 lizards exhibit this peculiarity in so marked a degree that 

 the generic name Cyclodus has been invented to express it. 

 Amongst extinct reptiles, also, a species of lizard from the 

 tertiary deposits of the Limagne in France, presents round 

 obtuse teeth, of which the last, in the lower jaw, is suddenly 

 and considerably larger than the rest. 



Notlwsaurus, Simosaurus, and Pistosaurus present the same 

 evidences of lacertian affinities in the division of the nostrils 

 by the median extension of the premaxillary backwards to 

 the nasals, the same thecodont dentition, and the same circum- 

 scription of the orbits and temporal fossae as in Placodus : 

 there is also a general family likeness in the upward aspect 

 of these apertures, accompanying an extreme depression of the 

 skull. The muzzle, though varying greatly in length in these 

 genera, presents the same obtuseness ; and the alveolar border 

 of the jaws the same smooth outward convexity which we 

 observe in the Placodus. The peculiar confluence of the 

 elements of the upper and lower zygomatic arches, — i. c, of 

 post-frontal and malar, — forming the broad wall of bone be- 

 hind the orbit, is continued still farther backwards in the 

 Simosaurus. In Pistosaurus the elongated post-frontal, malar, 

 and squamosal are united together in one deep zygomatic 

 arch, which has the mastoid and tympanic for its hinder 

 abutment. 



It is remarkable that hitherto no vertebrae or other bones 

 of the trunk or limbs have been found so associated with the 

 teeth of Placodus, as to have suggested their belonging to the 

 same species. Usually, after the indication of a reptile by 

 detached teeth, the next step in its reconstruction is based 



