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PROCEEDINGS OF THE NATIONAL MUSEUM 



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The nasals are as in R. stemhergii but relatively shorter. 



The frontals are differentiated only by the median and posterior 

 sutures. The posterior median line is less deeply indented by the 

 parietals than in R. stemhergii. 



The posterior extent of the parietal and its union with the supra- 

 occipital are faintly indicated as shown in figure 1, B. This surface 

 shows no indication of a sagittal ridge, which forms such a prom- 

 inent feature of the other species. 



In the palatal view none of the sutures can be determined ; the up- 

 ward pitch of the basisphenoid and parasphenoid surfaces is less 

 pronounced than in R. sternbergii. The posterior limits of the large 

 scalelike pterygoids can be clearly determined as shown in figure 1, C. 

 Their junction with the palatines, however, is fully coalesced and 

 cannot be determined. The anterior palatal region is hidden by the 

 articulated lower jaws and is therefore not available for study. 



Lower jaws. — The lower jaws remained in an articulated state, but 

 only the dentary and coronoid sutures show clearly, all others being 

 fused. Compared with the ramus of R. stemhergii^ the jaw is slend- 

 erer and the coronoid has a more anterior position, thereby making 

 the postcoronoidal part of the ramus considerably longer. The 

 number of teeth in the lower jaw cannot be determined from tliis 

 specimen. 



Table 1. — Comparative measurements of skulls of Rhlneura 



Measurement 



Greatest length at center 



Greatest width across squamosals 



Greatest width across orbits 



Least width of brain case 



Length of lower jaw 



Space occupied by upper teeth 



R. minutus 



U.S.N. M. no. 



12158 (type) 



Mm 



7.8 

 3.3 

 2.9 

 1.6 

 5.0 

 2.0 



R. sternbergii 

 (type) 



Mm 

 8.0 

 4.0 

 3.0 

 1. 7. 

 4. 1 

 2.0 



R. hatcherii 



P. M. no. 



11309 (typo) 



Mm 

 13.5 

 5.7 

 4.0 

 3.2 

 8.75 

 3.3 



Vertebrae. — There are 23 articulated vertebrae preserved with this 

 specimen. The anterior end of the series was in contact with the 

 skull. The first two vertebrae, however, are damaged, and they can- 

 not be positively identified as being the atlas and axis. In fact, the 

 absence of hypapophyses indicates that a few vertebrae may be 

 missing from the anterior end of the series. Except for their very 

 much smaller size, I am unable to detect any features that would 

 distinguish these vertebrae from those of R. hatcherii which I have 

 previously described.- The series has a greatest length of 31 mm. 



• Mem. Nat. Acad. Scl., vol. 22, p. 43, 1928. 



