collection, is now the property of the Indiana State University at Bloomington, Ind. 

 I will here refer to that specimen as the Owen specimen. The other, discovered by 

 Dr. M. W. Dickeson, belongs to the Philadelphia Academy of Sciences. I will call 

 it the Dickeson specimen. These two skulls and the Kansas specimen now before me 

 are, as far as known, the only Megalonyx skulls hitherto preserved in any collection. 

 The Kansas specimen is specifically distinct from the other two, and has also in 

 other respects a particular value, in so far as it shows the structure of the entire zygo- 

 matic arch and of the turbinals, which bones were nearly destroyed in the specimens 

 described by Dr. Leidy. This paper will, therefore, supplement his as a memoir on 

 the genus Megalonyx. For easier comparison with Dr. Leidy's figures, the figures 

 illustrating this paper have been drawn, with few exceptions, to the same scale as his. 

 They were executed by my old friend, Mr. A. M. Westergren, for twenty-five years 

 the able artist in the Royal Swedish Academy of Science, in Stockholm, now with 

 Prof. Alexander Agassiz, of Harvard. 



Judging from the more perfect obliteration of the sutural connections in the 

 Dickeson specimen, Dr. Leidy has demonstrated that it belonged to an older indi- 

 vidual than the Owen specimen. The same argument places the age of the Kansas 

 specimen between the other two. The sagittal and occipito-parietal sutures are less 

 open than in the Owen specimen, but more so than in the Dickeson specimen. The 

 temporo-parietal sutures are entirely obliterated, and so is the suture between the 

 basi-occipital and the basi-sphenoidal bones, both of which sutures are distinct in 

 the Owen specimen. 



Lateral view. — The obvious difference in the sagittal contour in the thi-ee skulls 

 (compare PI. I with Leidy's PI. I and PI. IV) may be explained as owing to differ- 

 ence in age, and would then confirm the conclusion derived from comparing the 

 sutural connections. The still more strikins: difference in the facial contour in the 

 two specimens of M. jeffersoni is most likely a secondary sexual chai-acter. May it 

 not be that the males of these animals, like those of the recent cystophorine seals, had 

 some special adaptation of their nose for vocal purposes ? The Kansas specimen 

 agrees in this contour more closely with the Dickeson specimen than with the Owen 

 specimen ; the latter having the nasal vault raised higher than the cranial portion, 

 which is not the case in the other two. It may thus be inferred that these two are 

 females, the Owen specimen a male. 



As stated above, but little remains of a zygomatic arch in the two specimens of 

 M. jeffersoni. A special interest attaches to this arch on account of its extreme 

 diversity of form in the difiei'ent genera of Edentates. Reinhardt* inferred from the 



* Prof. J. Reinhardt : " Ksempedovendyr-Slaegten Cmlodon;" Copenhagen, 1878, pp, 325, 326. 



