Vol. XXIX, pp. 125-128 June 6, 1916 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



\' 



GENERAL NOTES. 



"vv. 



NOTES ON THE GENERA ISOTHRIX WAGNER AND PHYLLOMYS 



LUND. 



Various species of Loncherinpe with soft or bristly (not spiny) pelage 

 are currently referred to the genus Isothrix Wagner, but little attention 

 has been devoted to cranial or dental modifications and such assignment 

 seems, in several instances, open to question. 



The genus Isothrix, as originally proposed by Wagner,* included three 

 species : /. bistriala, I. pachyura, and I. pagurus, but no type was men- 

 tioned and I am unaware that one has been fixed upon by subsequent 

 authors. The skull of /. pachyura was unknown to Wagner and the 

 other species, while apparently congeneric, differ appreciably in dentition 

 as figured by him.t In order, therefore, to abolish the resulting un- 

 certainty, the first species listed, Isothrix histriata ( Natterer MS. ) Wagner, 

 from the Rio Guapore and the Rio Negro is selected as the type of the 

 genus Isothrix Wagner. 



Comparison of the dentition of species ranging in Panama with this 

 type (1. c. ) reveals apparently important differential characters, especially 

 the complete transverse divisions of the molar crowns which persist until 

 advanced age, instead of the irregular reentrant angles and enamel folds 

 characterizing the genera Isothrix and Loncheres at similar stages of wear. 

 While these species differ from Isothrix, and from Loncheres as typified 

 by L. cristatus (Desmarest),t close agreement in dentition with Phyllomys 

 Lund is evidenced by comparison with figures accompanying his second 

 account. § This generic name based on material from bone caves in 

 southern Brazil, and treated by authors as synonymous with Loncheres 

 Illiger, seems available for a group transcontinental in distribution. The 

 Brazilian species of this group figured by Winge|| as Loncheres armatus 

 and said to have broad spines mixed with the fur, strikingly resembles 

 Loncheres labilis Bangs and Isothrix darlingi Goldman in cranial details. 

 The latter species differs in color and the dorsal armature is composed of 

 narrow, finely grooved bristles instead of broad spines, characters appar- 



* Wiegmann's Archiv. Naturgesch., 1845. Bd., I, pp. 145-146. 



tSchreber's Saiigthiere, Suppl. Ill, p. 335, Taf. 239 D, fig. 5. 



t Type fixed by Allen, Bull. Amer. Mus. Nat. Hist., N. Y., XII, p. 258, 1899. 



$K. Danske Vidensk. Selskab., Kjobenhavn, Vlll, 243-244, pi. 21, figs. 12-13. 1841. 



li E Museo Lundii, III, 1888. pp. 71. 80, pi. VI. figs. 3-4 and pi. VII. figs. 14-15. 



27— Pkoc. Biol. Soc. Wash., Vol. XXIX, 1916. (125) 



