Notices of Memoirs — if. Saiivage on Mosasaiman Beptilia. 465 



11. — On the presence of a Ebptile of the Mosasaueian type 

 IN THE Upper Jurassic Formations of Boulogne-sur-Mer.^ 



By M. H. E. Saxtvage. 



THE most ancient Mosasaurian known is the Geasaurus Scsmmer- 

 ringii, of Monheim and Solenhofen. This last-named locality 

 belongs to the Lower Kimmeridgian ; nor have any been heretofore 

 noticed higher up in the Jurassic series. Ee-appearing in the Green- 

 sand of New Jersey (where we find Geosauriis MitcJielli, and Mosa- 

 saurus Maximiliani), this type is extended to the Lower Chalk by 

 the Mosasaurus Hofmanni and M. gracilis. There is then a break in 

 the life of the Mosasaurian type, but only an apparent break, for the 

 types are always continuous throughout the whole period; they 

 never disappear entirely, and then re-appear higher up : such breaks 

 are only the result of the imperfect state of our knowledge. 



Prof. Owen has published, under the name of Leiodon, a reptile of 

 the Mosasaurian type, characterized by its teeth, of which the inside 

 is as convex as the out, and whose crown, of an elliptical form, is 

 bordered on each side by a sharp edge. 



The only known species, Leiodon anceps, occurs in the Chalk of 

 Norfolk and of Meudon. It is to this genus Leiodon that the teeth, 

 and a fragment of jaw found in the Middle Portland Marls of Portel, 

 near Boulogne, and in the clays which form the Upper Kimmerid- 

 gian, belong : this genus is also found a little lower, namely, in the 

 zone of Ammonites longispinus of the Middle Kimmeridgian. The 

 genus Leiodon appears then almost as early as the genus Geosaurus, 

 and has lived during the Upper Jurassic epoch, along with the 

 Steneosauri, the Pliosaurus, Megalosaurus, and Pterodactyle ; we 

 have, in fact, found these genera again in our Kimmeridge and Port- 

 land strata. 



The species which we propose to name Leiodon primcevum is 

 characterized by smooth strong teeth, more or less large and curved, 

 according to the place which they occupy, with faces regularly 

 convex, separated on each side by a strong sharp cutting edge run- 

 ning from the base to the crown, which is pointed. The largest 

 teeth are 65 millimetres high, the diameters near the base being 

 25 X 18. As M. P. Gervais has remarked, it is wrong that " they 

 described the teeth of the Mosasauri as really acrodont, like those of 

 many of the true Saurians." In our Leiodon the teeth are inserted 

 in large and deep sockets, which occupy nearly the whole depth of 

 the jaw ; the root therefore is closely united to the body of the bone 

 by the bed of cement which surrounds it ; the pulp-cavity is filled 

 with a mould of calcareo-siliceous matter, arising from petrifaction ; 

 this cavity, which regularly and imperceptibly contracts, runs from 

 the base of the root to near the crown of the tooth ; extending to a 

 little above the half of the latter. The Pterygoid bones were very 

 probably furnished with smaller teeth, one of the faces of which is 

 visibly flatter. 



^ Read at the meeting of the Aoad^mie des Sciences, July 10th, 1871. 



VOL. VIII. — NO. LXXXVIII. 



