14 



FOSSIL WISHES. 



The dentition of Cestracion (Figs. 14 and 15) shows it to have 

 been admirably fitted for the prehension and mastication of Crus- 

 tacea and Mollusca ; the teeth are seen to be arranged in oblique 

 rows upon the cartilaginous jaws and to vary greatly in character 

 between those forming the anterior series, which consists of sharp- 



Fig. 15.— Side-view of jaws of Port-Jackson Shark, Cestracion Phttippi (recent). 



pointed teeth modified for seizing and holding their prey, and the 

 lateral series, which is well adapted by their flattened form for 

 crushing the shells of Mollusks and Crabs. 



These lateral teeth also vary greatly in the several rows (see Pig. 

 14, a, £, c), covering the two rami of each jaw, and they enable the 

 palaeontologist clearly to understand that many so-called species 

 founded on different forms of fossil palatal teeth found detached 

 from one another, may, after all, have really belonged to different 

 parts of the mouth of one and the same individual species of Shark. 



Fie. Hi.— Teeth of Cochliodus contort a*, 

 Carboniferous Limestone, Armagh. 



FlG. 17. — Some of the central teeth of Janassa 

 I ingucuformis, Coal-measures. 



The two dorsal fins also were each armed with a short but strong 

 spine. Similar spines are frequently met with in the same series of 

 deposits in which the palatal teeth have been discovered. 



Table-cases 29, 30, and 32, well illustrate the modifications of form 

 observable in the teeth of such geuera as Psephodus, Orodus, 

 Streblodus. Cochliodus (Fig. 16), Sandalodus, Psammodus, Petalodits, 



