EVIDENCE BEARING ON TOOTH-CUSP DEVELOPMENT 93 



Woodward 1 found that in Ccntctcs and Ericulus the main in- 

 ternal cusp, usually termed the protocone, was first to develop, 

 but he believed this cusp to be the paracone, the whole tooth 

 representing only the antero-external triangle of such a form 

 as Talpa, the protocone and metacone not having been de- 

 veloped. This, as stated by Woodward, is a modification of 

 Mivart's view published in 1868, 2 in which he states his belief 

 that in Ccntctcs, Chrysocloris* and like forms, the main 

 portion of the crown represents the union of the two external 

 prisms of Talpa and like forms. According to Mivart, the 

 main internal cusp of Ccntctcs, Ericulus, Chrysocloris, etc., 

 was derived by the fusion of the paracone and metacone, while 

 the protocone and hypocone are wanting or rapidly diminishing 

 in size and importance. According to both Woodward and 

 Mivart, therefore, in these forms, which have been considered 

 typical trituberculates, the outer cusps are developments of the 

 cingulum, while the main internal cusp has been wrongly termed 

 the protocone and is in reality the paracone, according to 

 Woodward, or combined paracone and metacone, according to 

 Mivart, while the inner cusp (protocone) is greatly diminished in 

 size or has entirely disappeared. These two authorities, there- 

 fore, are agreed on the two points of principal importance regard- 

 ing Ccntctcs and Ericulus, viz : (1) the location of the paracone in 

 the main internal cusp and (2) the ultimate loss of the protocone. 

 I strongly concur in these views, for in a series of upper molars, 

 including Potamogalc, Solcnodon, Ccntctcs, Ericulus, Hcmi- 

 ccntctcs and Chrysocloris (see figs. 1-6, pi. IV), the stages sug- 

 gesting the gradual diminishing and final disappearance of the 

 protocone are very complete, amounting almost to demonstration, 

 and there can be little doubt that the molars of the Ccntctcs and 

 Chrysocloris type have been derived from forms similar to that 

 of Potamogalc, involving the loss of the protocone. In conse- 

 quence of this the paracone, or combined paracone and meta- 

 cone, comes to be the principal inner cusp. In Potamogalc the 



1 Proc. Zool. Soc. London 1S96, 588-589. 



2 Journ. Anatomy and Physiol., Vol. II, 139, 1S6S. 



3 The form figured by Mivart has since been removed to a distinct genus, 

 Bematiscus Cope, Am. Nat., XXVI, 1S92, 127. The typical Chrysocloris upper 

 molar has no trace of a protocone. 



