On the Lower Jaw 0/ Stereognathus ooliticus. 07 



I X. — Note on the Lower Jaw <y' Stereognathus ooliticus, 

 Charlesworth. tiy Dr. Bbanislav Petbonievics. 



[Plate III.] 



In 1854 Charlesworth announced the discovery of the fragment 

 of jaw of*a new mammal, to which he gave the name Sttreo- 

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

 figured. In 1887 Marsh expressed doubts about the nature 

 of the fragment, suggesting the possibility of its being an 

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

 before *. 



To 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 by 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 magnify ing-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. III. fig. 4, a, /3, 7), corresponding to 

 the three longitudinal rows of cusps. 80 that we have in 

 Stereognathus only a transverse division of molar roots. 



PI. III. fig. 1 shows the outer side of the 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 he 



* Comp. 'Marsh, O., 1887, p. 343: "None of the known Mesozoic 

 mammals appear to have been truly herbivorous. Stereognathus, which 

 has been considered as such, from its molar teeth, cannot fairly be re- 

 garded as evidence, since it was based, not upon part of a lower jaw, as 

 described by Owen, but upon a fragment, evidently the posterior portion 

 of the maxillary, and the teeth resemble the superior molars of some 

 insectivorous forms." Comp. also Marsh, 1891, p. 613. 



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

 " The outer side of the crown (hg. 115, b), supported by a bifurcate lung 

 which contracts as it sinks into the socket, shews ....'' 



