124 Bulletin American Museum of Natural History [Vol. LXXII 



two of which no canine is present. In the two others, however, a canine 

 is retained on one side. 



SOME CHARACTERS UTILIZED FOR CLASSIFICATION OF HYRACOIDEA 

 AND THEIR VARIATION IN THE CONGO SPECIES 



Cranial Characters 



Because Hahn's monograph treats exhaustively of the value of most 

 commonly used skeletal characters it would be superfluous for me to dis- 

 cuss them in general, but the series which I have studied have furnished 

 some information not covered by Hahn or at least neglected by him. 

 Some of this is here recorded. 



Closure of the Orbits 



No specimen of either Procavia j. lopesi or Heterohyrax chapini in the 

 Congo Expedition collection has closed orbits. Every skull of Dendro- 

 hyrax d. emini examined has closed orbits, even in Stage I. In this re- 

 spect all specimens are in harmony with their generic standard. In 

 many other species of hyrax such constancy does not obtain. 



Length of Diastema 



Diastema length, as I have noted above and as may be clearly seen 

 from an examination of the table of cranial measurements, is subject to 

 too great variation in equal aged individuals of the same sex, from the 

 same locality, to be a reliable criterion as to race. Generic differences 

 are well marked, it is true, and occasionally specific differences. The 

 length of the diastema increases with age, both actually and relatively, 

 in most, if not in all species. 



The Course of the Temporal Ridges 



The course of the temporal ridges in my experience, although Brauer 1 

 believed otherwise, has proved totally inconstant in every species of 

 hyrax examined in series. Among equal-aged specimens of one sex of one 

 species (e. g., D. d. emini) are found ridges that are parallel along the 

 greater part of their superior border; others strongly bowed and most 

 nearly approximate at the middle of the parietal ; others which converge 

 sharply from the anterior end of the parietal to its posterior border. 

 For this reason I do not consider the pattern as indicative of genetic 

 relationship. 



i 1934, Zeitschr. fur Saugetierkunde, Bd. IX, pp. 198-206. 



