PLESIOSAURIDiE. 



Polyp tychodon interruptus, Owen l . 



173 



The type species 2 . Typically the ridges on the enamel of the 

 teeth (fig. 58) placed at a considerable distance apart, and a large 

 number of them, especially on the convex side, not extending to the 

 summit. Other teeth show a transition to the next form. 



The horizon of the type specimen is not mentioned. 



Hab. Europe (England, France 3 , Germany *, Bohemia 4 , and 

 liussia *). 



Fig. 58. 



Poh/ptychodon interruptus. — Tooth; from the Cambridge Greensand. },. A 

 portion of the enamel of the crown is shown on the right, of the natural 

 size. 



The following specimens are from the Upper Chalk ; in many of 

 them the ridges on the enamel are more approximated and finer 

 than in the specimens from the Cambridge Greemand. 



49011. The right half of the anterior extremity of the mandibular 

 {Fig.) symphysis, showing one entire tooth of medium size and 

 the alveolus of a second ; from Kent. Figured in Dixon's 

 'Geology of Sussex,' 1st ed. pi. xxxviii. fig. 3, and also 

 by Owen in his 'Cretaceous lleptilia' (Mon. Fal. Soc), 

 pt. i. pi. x. fig. 7 (1851). Purchased*, 1878. 



1 Odontography, Alias, pt. ii. p. 19, pi. 72. fig. I (1841). 



2 The name P. continuity occurs first in the original description, but it seems 

 preferable to take the present and better known form as the type. 



3 Sauvage, Mem. Soc. Gtol. France, s6r. 3, vol. ii. art. 4, p. 27. 

 1 Vide infra. 



