126 EVOLUTION OF MAMMALIAN MOLAR TEETH 



distinct cusps in Myo;/ale (Fig. 69 F}, and the intermediate conules- 

 (pl, ml) are very prominent in Galcopithecus (Fig. 69 G). It is these 

 confusing elements which have led to the proposal of such diverse 

 homologies by different authors. Mr. Gidley interprets the cusp 

 homologies as follows: In Fig. 69 A-I the cusps marked ps, pa, ms, 

 ms", me, mts are all peripheral or stylar cusps, none of them 

 homologous with the paracone and metacone of other mammals. In 

 A, C, D the cusps marked pr are really paracone or paracone + metacone, 

 the protocone being represented by the internal ledge marked hy. 

 In E-I the ledge-protocone is fully established. In E the cusps 

 marked pi, ml are really the paracone and reduced metacone. On 

 this interpretation A, C, D, instead of being primitive, represent a 

 secondary simplification by fusion of the paracone and metacone. 

 This interpretation also harmonizes with the probability of an inward 

 displacement of the para- and metacones in F-I, as in many genera, 

 (Cf. Figs. 67, 75, 83, 85 (m 3 , m 2 ), 90, 94, 116, etc.) Again, the molar 

 pattern of Ictops acutidcns tends to connect the tritubercular pattern of 

 Ictops thomsoni, with the quadritubercular pattern of Erinaceus and 

 higher types, but it does not justify the identification of the main 

 internal cusp as homologous in modern Zalambdodont and Dilambdodont 

 Insectivores. 



The teeth of Insectivora, therefore, require thorough re-examin- 

 ation on the basis of the tritubercular theory to test these disputed 

 points. (See Addendum, page 225.) 



For those to whom the original materials are not accessible, the 

 following references to works which contain numerous figures will be 

 especially valuable : 



SPECIAL REFERENCES. 



FIGURES OF TEETH OF INSECTIVORA. 



Bronn, H. G., Klaus, u. Ord. d. Thierreich's, Bd. I., pp. 202-211, 233 (Galeopithecus). 



Dobson, G. E., Monograph of the Insectivora, Pt. I. 4to. 1882. 



Owen, E,., Odontography, 1840-45. 



Tomes, C. S., A Manual of Dental Anatomy, 1898. 



De Blainville, Osteographie des Mammiferes. (See esp. " Cladobates," Tupaia.) 

 Paris, 1839-64. 



Schlo?ser, M., Die A /en. . . . Insectivoren . . . des Europaischen Tertiary etc. 

 Wien, 1887-90. 



Leche, W., Zur Morphologic des Zahnsystems der Insectivoren. Anat. Anz., Bd. 

 XII., 1897, p. 513. 



Leche, W., Zur Entwickelungsgeschichte des Zahnsystems der Saugetiere. Stuttgart, 

 1895. 



Matthew, W. L)., "The Fauna of the Titan otherium Beds at Pipestone Springs, 

 Montana," Bull. Amer. J//w. Nat. Hist., Vol. XIX., 1903, pp. 197-226; "A Fossil 

 Hedgehog from the American Oligocene," Bull. Amer. Mus. Nat. Hist., Vol. XIX., 

 1903", p. 228 ; " Fossil Mammals from the Tertiary of North-eastern Colorado," 

 Mem. Amer. Mus. Nat. Hist., Vol. I., Pt, VII., pp. 375-376. 



