56 PBOCEEDINGS OP THE GEOLOGICAL SOCIETY. [Apr. 20, 



present species resembles the Ptychognathus in the length of the face, 

 and more especially the Pt. declivis and Pt . latirostris in its direction 

 and in the relative position of the ridge representing the canine's 

 socket to the nostril. In Oudenodon Bainii this ridge is behind the 

 nostril ; in the present species it is beneath it, and is more horizontal 

 than vertical. 



The orbits have the same oblique aspect, upward and outward, as 

 in Oud. Bainii, but their longitudinal exceeds their vertical diameter ; 

 the nostrils have a similar longitudinally oval shape, and are more 

 directly in advance of the orbit ; the supernarial tuberosity is rela- 

 tively larger. The maxillary ridge is more angular and more pro- 

 duced, besides being continued more obliquely forward. The corre- 

 spondingly produced and sloping part of the premaxillary is nearly 

 straight, and is strengthened, as in Ptychognathus, by a low median 

 obtuse ridge. The maxillary ridge subsides below, to the edentulous 

 alveolar border, rather more gradually than in Oudenodon Bainii, its 

 outer longitudinal contour forming a gentle convex curve ; these ridges 

 give a very peculiar feature to the present skull. The fore part of the 

 premaxillary does not descend so nearly to the level of the maxillary 

 alveolar process as in the Oudenodon Bainii, and consequently the 

 symphysis of the mandible is more produced and curved upward, which 

 is another feature of resemblance to Ptychognathus in the present 

 skull, — the depth of the symphysis here exceeding the same diameter 

 of the opposed fore part of the upper jaw. The symphysis is narrower 

 in proportion to its length than in Ptychognathus ; its fore part is 

 slightly produced along the middle line, resembling a low ridge. The 

 vacuity between the dentary and angular elements is long and 

 narrow ; it is overarched by a slight ridge. 



Oudenodon Greyii, Ow. 



A third species of Oudenodon, with maxillary ridges as in 0. 

 prognathus, has a less elongated cranium and temporal fossae, more 

 rounded orbits, and a narrower interorbital space. It forms part of 

 the collection transmitted by Sir George Grey, to whom the species 

 which it indicates is dedicated. 



Hyoid apparatus of Oudenodon. (PI. III. fig. 5.) 



In an obliquely crushed specimen of the skull with the lower jaw 

 of the Oudenodon Greyii there are several bones, constituting a 

 symmetrical apparatus in the position of the hyoid, beneath and 

 between the rami of the lower jaw, where they are evidently in 

 advance and rather to one side of their proper position. The hind- 

 most, on the middle line (fig. 5 43), is best preserved. It is broad, 

 flat, and very thin, of a symmetrical semicircular form, with a pro- 

 duction like a stem from the middle of the straight side, which is 

 directed forward. This stem is partly underlapped by the median 

 end of a pair of long, narrow, flattened bones (ib. 45), which proceed 

 transversely outward, slightly expanding to that end. Their anterior 

 border is straight, the posterior border is slightly concave. 



