54 Placodontia Anomodontia. 



and the lower jaw presents a similar strong development of the 

 coronoid process. This powerful action of the jaws for biting 

 and grinding relates to the form and size of the teeth, which 

 resemble paving-stones, and were evidently adapted to crack 

 the shells of Mollusca, Crustacea, and perhaps Echini also, 

 upon which this reptile probably subsisted. 



The upper jaw contains a double series of these teeth, an 

 outer, or maxillary series, and an internal or palatal series ; 

 but the under jaw has only a single row of teeth. 



Although now admitted to be a reptile, this remarkable 

 genus was formerly classed by Minister and Agassiz as one 

 of the Pycnodont fishes. 



Placodus. Placodus gigas (Agassiz) . A closely allied form ; ha,s a more 



Table-case, elongated cranium with a distinct premaxillary rostrum carrying 

 No. 17. three chisel-like teeth on each side. It has three polygonal 



FIG. 74. Cyamodus (Placodus) laticeps (Owen). A, palatal aspect ; B, frontal aspect 

 of cranium ; from the Muschelkalk of Baireuth, Germany. (Table-case, No. 17.) 



palatine teeth and four or five maxillary ones. The cranium is 

 more elevated than in Cyamodus. 



Order XI. ANOMODONTIA. 



Wall-^ases, In this order the limbs are adapted for walking. The 



skull is comparatively short ; the quadrate bone is fixed ; a 

 parietal foramen is present : there is one temporal arcade ; 

 the nasals are large ; in the palate the pterygoids meet 

 together in front of the basispheiioid, which they also 



