1888.] 



NATURAL SCIENCES OF PHILADELPHIA. 



299 



menclature. As the writer anticipated after examining Prof. Marsh's 



Dryolesies, (Am. Naturalist^ 

 March 1888, p. 234 and Mem- 

 oir, p. 236.) the genera Amblo- 

 therium and Aehyrodon prove 

 upon further examination and 

 exposvire of the crowns to be- 

 long to the Stylodon type. 



It further appears that Mr. 

 Lydekker was correct in plac- 

 ing Peraspalax with Ainblo- 

 thermm (op. cit., p. 275), 

 although he did not recognize 

 the trituberculate character 

 of the crown with the styloid 

 external cone and two internal 

 cusps and heel. The writer 

 was in error, first in describ- 

 ing the external cusp of the 

 molars of this genus (Peras- 

 palax) as separated by a valley 

 from the internal cusps, for 

 there proves to be a distinct 

 transverse crest; probably also, second, in associating this jaw with 

 the Peralestes maxilla, (op. cit., p. 233). 



It is now evident that the molars of Professor Owen's types of 

 Amblotherlum soricinvm (Mes. Mamm., 1871 p. 29) of ^1. mustelula 

 (ihid.,p. 31.), of Phasct)Iestes longirostris (ibid., p. 35.), of Aehyrodon 

 nanus (ibid., p. 37.), of A. pnsillus (ibid., p. 39.), of Peraspalax; 

 talpoides (ibid., p. 40.), all present substantially the same crowns, 

 (see Fig. 2). It is also^probable, but not actually demonstrated, that 

 Sfi/lodon pusillus (Geol. Mag., 186G, p. 199.) and S. robiistus (ibid.) 

 have the same molar pattern. Professor Marsh has further applied a 

 series of generic and specific names to the closely allied American 

 genera. Altogether it will prove a difficult matter to clear up the 

 synonomy of these numerous species and will require a close exam- 

 ination and revision of all the material available. 



It is singular, in view of the probable similarity of many of these 

 species, that all the specimens referred to Stylodon, because exposing 

 the external face, possess but seven molars, with one possible excep- 



Fig 2. 

 a, Kiirlodon. Superior molar series of 

 the left maxilla, viewed upon the wearing 

 surface, b, Antblotherium soricinttm, infe- 

 rior molar series, viewed from above. In 

 A. [Peraspalax) talpoides. A lower molar 

 viewed upon the internal face. c. The 

 same. A lower molar viewed from above. 

 d, Aehyrodon nanus. A lower molar 

 viewed from above. Much enlarged. 

 Abbreviations as in lig. 1. 



