Placodontia. 
53 
Order X.— PLACODONTIA (Plate- toothed Reptiles). 
The genus Cyamodus, from the Muschelkalk of Germany, Cyamodus. 
offers a remarkable modification in its dentition not usually Table-case, 
met with in the reptilian class, but of which the class of fishes No- 18, 
affords numerous examples. The skull is as broad as it is 
long, the greatest breadth being behind, whence the sides 
converge to an obtuse muzzle. The temporal fossae are the widest 
and the zygomatic arches the strongest in the reptilian class, 
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 
and bruise shells of Mollusca, Crustacea, and perhaps Echini 
also. (Owen.) 
A B 
Fig. 73 . — Cyamoclus ( Placodus ) laticeps (Owen), a, palatal aspect; b, frontal aspect 
of cranium ; from the Muschelkalk of Baireuth, Germany. (Table-case, No. 18.) 
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 Munster and Agassiz as one 
of the Pycnodont fishes. 
Placodus gig as (Agassiz). A closely allied form ; has a more Placodus. 
elongated cranium with a distinct premaxillary rostrum carrying 
three chisel -like teeth on each side. It has three polygonal 
palatine teeth and four or five maxillary ones. The cranium is 
more elevated than in Cyamodus. 
