CYCLOPIDIUS 



253 



Specific Characters: In my opinion, arrived at several years ago, the differences between this 

 species and C. simus are not in the main too great to be explained on the basis of age and sex. 

 Recently Schlaikjer (1935, p. 166) enumerated Cope's distinctions between the two and showed that 

 he also came to the same conclusions as I did. However, there is a difference in the position of the 



Fig. 180. — Cyclofidius emydinus Cope. 



Superior view of skull. HT. 

 (After Cope, 1888.) 



Cat. No. 8115 A.M.N.H. 3/5 nat. size. 



palatonarial border, which in C. emydinus lies several millimeters behind the line of the posterior 

 edges of the last molars. Schlaikjer says this "might also be accounted for as an old age character, 

 or an individual variation." In all of the other known skulls of this genus the palatonarial border 

 lies on the line across the posteriors of M 3 , or slightly in advance of it. If we had more skulls, they 

 might show that this is a valid specific character. It has been shown that the molars in this genus 



Fig. 181.— Cyclofidius emydinus Cope. Skull. HT. Cat. No. 8115 A.M.N.H. 3/5 nat. size. (After Cope, 1888.) 



usually change a little with old age in the relative proportions of width and length. The type of 

 C. emydinus, an old individual, has an index of 1.46 for M 1 , while the same in C. simus, a much 

 younger animal, although fully adult, is 1.12. If care is exercised in measuring these teeth to obtain 

 the maximum dimensions, not just those of the grinding surface, these variations will probably not 

 change markedly during the adult life of the individual. I should look for the broader, heavier 

 teeth in a male. The type of this species is also heavier, and some of the bones are more rugose, 

 which can be explained on the basis either of age or male sex. The skull index of this species, as 

 well as that of C. simus, is approximately 0.71. By far the majority of characters of this species 

 and of C. simus are alike or exceedingly close, and, until more evidence is at hand, I prefer to con- 

 sider this as a synonym of C. simus. 



