183 



Dr. Hays called the attention of the Society to an abstract, 

 recently published, of a paper read by Prof. Owen to the Geo- 

 logical Society of London, relative to Mr. Koch's collection of 

 mammalian remains. c 



Prof. Owen, it is stated, by a series of comparisons of the lower 

 jaws in that collection, has "arrived at the conclusion, that the Te- 

 tracaulodon of Godman is the immature state of both sexes of the 

 Mastodon giganteum, and that it loses these distinctions in the mature 

 state of both sexes, by the loss of one tusk in the male, and by the 

 loss of both in the female." 



Prof. O. conceives, that these views are supported by analogies, and 

 he refers to the Dugong and Narwhal as examples. In the former, 

 in both sexes, the lower jaw is provided, at its deflected extremity, 

 with six incisors, which disappear in the mature animals, one or two 

 abortive remnants at most being occasionally discovered hidden in 

 the irregular cancellous sockets. In the male Dugong the upper in- 

 cisors are protruded, scalpriform, and of unlimited growth; while in 

 the female they are concealed, cuspidate, and solid at their base, 

 which is expanded. 



In the Narwhal, the young of both sexes have a single incisor 

 equally developed on each side of the upper jaw ; one of which grows 

 rapidly in the male, constituting the well-known spirally twisted tusk, 

 while the other remains stationary ; and both continue rudimental 

 in the female. 



Dr. Hays awarded to Prof. Owen's theory the merit of being very 

 ingenious, of embracing all the facts presented by the collection of 

 Mr. Koch, and of explaining several difficulties which had hitherto ex- 

 isted ; still he conceived that it was founded on too limited observa- 

 tions to challenge our implicit credence. A complete series of jaws 

 of both sexes and of all ages, which is necessary to settle this ques- 

 tion, has never yet been brought to light, and Dr. H. could not, there- 

 fore, refer the Society to any specimens which refuted the above the- 

 ory ; but still he would invite the attention of the Society to some, 

 which, at least, created strong doubts of its entire correctness. 



Dr. H. then exhibited two casts, one representing the chin and 

 right side of a lower jaw, belonging to the museum of the University 

 of Virginia, figured in Vol. IV. N. S. pi. XXVII, of the Society's 

 Transactions ; the other, the left side of a lower jaw, in the Wistar 

 Museum, and figured in Trans. Vol. IV. N. S. pi. XXI. Both of 

 these had appertained to animals of the same age and adolescent 

 (having two molars only left, the ultimate and penultimate ones) ; yet 



