118 



ON THE EXTINCT MAMMALIA OF 



of Oreodon. (Compare figures 1 — 11, plate XI, with figures 1, 2, plate VI, figure 1, 

 plate VII, and figure 1, i:)late VIII.) 



If one can judge from the jaws, the general form and construction of the skull of 

 Merychyiis is the same as in Oreodon. 



The alveolar portion of the upper jaw, as seen in figure 1, plate XI, has the same 

 form as in the latter, but at the border is more convex antero-posteriorly. The infra- 

 orbital foramen occupies a position above the fourth premolar; in Oreodon it is placed 

 above the third premolar, and in Merycochcerus above the interval of the first and 

 second true molars. 



The lower jaw, as represented in figure 2, plate XI, has the same form as in 

 Oreodon, except that its alveolar border is more sloping from behind, and it is more 

 convex obliquely across the back portion. 



It may be supposed that the genus Merychyus is an offspring of the earlier genus 

 Oreodon, and would appear to be a striking example of the theory of natural selection 

 of the eminently jjhilosophic Darwin. 



There appear to be three distinct species of Merychyus indicated by the fossils, and 

 mainly distinguished by their size. 



Merychyus elegans. 



The smallest species of Merychyus, to which the above name has been given, is 

 founded on several halves of upper and lower jaws, containing admirably preserved 

 series of teeth of two difierent individuals. Some of the specimens, with different 

 views of the teeth, are represented in figures 1 to 11, plate XI. They indicate an 

 animal intermediate in size to Oreodon gracilis and 0. Oulhertsoni. 



The measurements of the specimens are as follows : 



Distance from maxillary tuberosity back of alveolar border to 



alveoli, . . . . 



Breadth at infra-orbital foramina, 

 Breadth of hard palate between first true molars. 

 Depth of lower jaw at back of last molar. 

 Depth of lower jaw below last premolar. 

 Length of symphysis. 

 Length of upper molar series. 

 Length of lower " " . . 



Length of upper true molar series, 

 Length of lower " " 



Antero-posterior diameter of last upper true molar. 

 Transverse " " " 



incisive 



Lines. 



44 

 17 

 14 

 17 

 10 

 17 

 36 

 35 

 22 

 24 

 10 

 8 



