On the J. inrcr Jaw of Stereognathus ooliticus. 07 



[X. — Note on the Lower Jaw of Stereognathus ooliticus, 

 Charlesworth. I5y Dr. BbaniSLAV PetbONIEVICS. 



[Plate HI.] 



In 1854 Charlesworth announced the discovery of the fragment 

 oi jaw of a new mammal, to which he gave the name Stereo- 

 gnathus, and which afterwards, in 1857, Owen described and 

 figured. In l.s.s? Marsh expressed doubts about the nature 

 oi the fragment, suggesting the possibility of its being an 

 upper jaw instead of a lower one, as was held unanimously 

 befo*-* 



lore 



/''«» decide the question, I took, while in London at the end 

 of last year, the specimen from the Museum of Practical 

 Geology, where it, is preserved, to the Natural History 

 Museum, where it was further prepared \>y F. O. Barlow 

 according to my directions. 



When I saw the specimen for the first time, and compared 

 fig. 3 of the middle tooth in Owen (1857) with the root of 

 this tooth, I was struck by the inexactness of Owen's figure 

 (fig. 29, pi. i. in Owen,' 1871, is better in this respect). 

 Owen's figure shows a longitudinal division of the root, 

 whilst the magnifying-glass shows no trace of such a division, 

 and the root of the other side of the same tooth, now un- 

 covered, confirms this lack of division f. But the newly 

 prepared hindermost tooth shows on the hinder side three 

 distinct roots (comp. PI. [II. tig. 4, «, /3, 7), corresponding to 

 the three longitudinal rows of cusps. 60 that we have in 

 Stereognathus only a transverse division of molar roots. 



PI. III. fig. 1 shows the outer side of (he fragment. As its 

 vertical diameter is greater behind than in front, we must 

 conclude that the deeper end is the hind end of the jaw, 

 which, accordingly, is a left one. This state of things was 

 rightly referred to by Owen (comp. Owen, 1857, p. 2), but ho 



* Comp. Marsh, 0., 1887, p. 843: "None of the known Mesozoic 

 mammals appear to have been truly herbivorous. Stereognathus, which 

 has been considered as such, from its molar teeth, cannol fairly be re- 

 garded as evidence, since it was based, not upon part of a lower |.-. 

 described by Owen, but upon a fragment, evident!} the po n rior portion 

 of the maxillary, and the teeth r< emble the mperior molars of some 

 111 lectivorous forms." Comp. also Mai -I., 1891, p. 613. 



+ In his 'Palaeontology,' 2nd ed. 1861, p. 345, Owen says expressly : 

 " Iheouter ride of the crown (fig. L15, b), supported by a bifurcate fang 



winch contracts as it sinh into the socket, hev 



ft* 



