792 



THE MIOCENE FAUNA. 



and Soricidce. The first true molar of Scalops is a good deal like that of 

 Bidelphys, but the anterior cusp is larger, and tliere is no anterior interme- 

 diate cusp, while the posterior external is of reduced size. The posterior V 

 is better developed than in Bidelphys, but is composed in the same way, of 

 a posterior intermediate cusp, and a posterior external with a posterior heel. 

 These are united by stronger ridges in Scalops, Condylura, and Blarina than 

 in Didelphys. On the second true molar in Scalops a V represents the an- 

 terior external cusps of the first true molar. Whether this V has a consti- 

 tution like the posterior one, i. e., is composed of external and intermediate 

 cusps joined, is difficult to determine; but it is probably so constituted. It 

 seems to be pretty clearly the case in Blarina, where the fourth premolar 

 and first true molars may be compared, with a resulting demonstration of 

 the correctness of this view. In Condylura the Vs have become more de- 

 veloped and the external cusps reduced, so that the analysis is more difficult. 



This interpretation applied to Urotrichiis and Galeopithecus gives them 

 quadrituberculate molars, not trituberculate, as determined by Mivart. 

 Mystoniys is trituberculate. The intermediate tubercles are present, but 

 are imperfectly connected with the external, so that Vs are not developed 

 (vide figures of Mivart and Allman). This genus ofi'ers as much confirma- 

 tion of the homology here proposed as do the opossums, but it difi"ers from 

 the latter in having the anterior intermediate tubercle the larger, instead of 

 the posterior. Mystomys and Solenodon also confirm the determination 

 the internal angle of the crown in Centetes^ is the anterior internal cusp. 



In conclusion I give the following synoptic view of the constitution of 

 the superior molar teeth in various genera of the Bunotheria: 



'This view was first advanced by the writer in the Annual Report of the United States Geo- 

 logical Survey Territories, 1873 (1874), p. 472. 



