MASON DAKOSAURUS. 



219 



It is noticed by Prof. Owen*, who rightly includes it among his 

 *' amphica3lian " Crocodilia. 



Teeth of Bakosaurus are said to occur, associated with remains of 

 PUosaurus, Gyrodus, Sjyhcerodus gig as, &c., in the Potton Sands de- 

 scribed by Mr. Seeley ; these are its companions, both in the Upper 

 AATiite Jura of Schnaitheim and in the Kimmeridge Clay of England. 

 Mr. ^''alkert also mentions it as occurring in beds probably of the same 

 age at Upware, in the Pens of Cambridge, and in similar company. 



I have examined, through the kindness of Mr. "W. Davies, a suite 

 of the Potton fossils at the British Museum ; but it would be almost 

 impossible, owing to the worn condition of these fossils, which have 

 evidently been derived from older rocks, to determine with any de- 

 gree of certainty its presence among them. 



The British Museum contains numerous specimens of Dakosaurus 

 from the German locality, as well as a single tooth from the Kim- 

 meridge Clay of Boulogne and one from that of Ely, near Cambridge. 

 A comparison of these with the teeth from Oxford fails to discover 

 differences of specific value ; I therefore propose to retain M. Quen- 

 stedt's name of maximus for the latter. 



Fig, 3. 



Fig. 4. 



a. External view of tooth of Dakosaurus, the 



ridges forming the contour lines. Side view of an anterior 



b. The same tooth, showing the pulp-cavity. tooth of Dakosaurus. 



This genus is characterized by large, conical, incurved and slightly 

 recurved teeth, the smooth and polished enamelled crowns of which 

 are traversed by two sharp, prominent, minutely crenulated longi- 

 tudinal ridges, one forming the posterior, the other the anterior 

 margin of the tooth ; these ridges are situated '' midway between 

 the convex and concave curvatures of the tooth," which is compressed 

 at the apex so as to give in transverse section a slightly oval figure 

 pointed before and behind ; but this character dies away towards the 

 base, where the crown becomes cylindrical and ceases to be inter- 

 rupted by the ridges ; one of these, the anterior, is lost sooner than 

 the other, which is continued a short distance into the cement- 



* Palgeontology, 2nd edit, p 300. t Geol. Mag. vol iv. p. 309. 



