Lower Jaw 0/ Stereognathus ooliticus. 69 



the motion of its lower jaw from before backwards*. If this 

 mechanical explanation is a right one, then we may conclude 

 that the oblique position of molar cusps in Stereognathus (and 

 probably also in Menisc 'issus) is due to a motion of its i 

 jaw from backwards forwards, opposite to the direction in 

 rodents. 



Finally, I desire to express my thanks to Dr. A. Strahan 

 and \)\\ Kitchin, of the Museum of Practical Geology, and to 

 Dr. Woodward, of the British Museum, for the loan of the 

 new preparation. Also to Dr. Andrews, of the British 

 Museum, tor some valuable help. 



Literature on Stereognathu3. 



1. Charlesworth, E. '•' Notice on new Vertebrate Fossils," in Report 



of the British Association, 1854, Transactions, p. 80. 



2. < Iwk.v, it. " On the Affinities of the Stereognathus ooliticus (Charles- 



worth i, a Mammal from the Oolitic Slate of Stonestield," in Quart. 

 Journ. Geol. Sue. Loud. vol. xiii. 1857, p. 1-11. 

 8. Owbn, K. 'Palaeontology,' 2nd ed. 1861 ("On Stereognathus," 

 pp. 346-349). 



4. Owbn, 11. 'Monograph of the Fossil Mammalia of the Mesozoic 



Formations,' 1871 (on Stereognathus, pp. 18-20). 



5. Marsh, Ch. O. " American Jurassic Mammals," in Amer. Journ. Sci. 



vol. xx.xiii. 1887, pp. 327-348 (on Stereognathus, p. 343). 



6. Osbobn H. F. " On the Structure and Classification of the Mesozoic 



Mammalia," in Journ. Acad. Nat. Sci. Philad. 1888, pp. 186-264 

 (on Stereognathus, p. 221). 



7. Marsh, Ch. O. "Notes on Mesozoic Mammalia," in Amer. Nat. 



vol. xxv. 1891 (on Stereognathus, p. 613). 



8. Goodrich, E. S. " On the Fossil Mammalia from the Stonesfield 



Slate,'" in Quart. Journ. Micr. Sci. vol. xxxv. 1894, pp. 407-432 

 (on Stereognathus, p. 424, -with the note of E. Ray Lankester on 

 another lost fragment of jaw of Stereognathus). 



EXPLANATION OF PLATE III. 



Stereognathus, Charlesworth. 



tig. 1. The outer side of the fragment of lower jaw, somewhat mutilated 



in front. 

 lig. 2. The inner side of the same ; mg., mylohyoid groove. 



* Comp. Ryder, T. A., "On the Mechanical Genesis of Teeth-forms," 

 in Proc. Acad. Sci. Philadelphia, 1878, especially fig. 8b,f, p. 66, and 

 Cope, E. D., •' The Mechanical Causes of the Origin of the Dentition of 

 the Rodentia," in ' American Naturalist,' vol. xxii. 1888, p. 9 s. and p. 12 

 (also his ' Primary Factors of Organic Evolution,' 1904, pp. 349-351 and 

 p. 325). 



