SCIUEIDiE— EXTINCT SrECIES. 931 



with possibly one exception,* the remains from the Tertiary deposits of the 

 West belong to wholly extinct genera. The genera of this family, most abun- 

 dant in the Eocene deposits, and which may be unquestionably referred to 

 the Sciuridce, are Paramys and Sciuravus, which are not apparently very dis- 

 tantly related. The remains referred to these genera indicate species ranging 

 in size from animals smaller than Sciurus hudsonius to those one-fourth larger 

 than Arciomys monax. Other apparently Sci urine forms are the genera Tax- 

 ymys Marsh, Tillomys Marsh, Heliscomys Cope, and possibly Colonomys 

 Marsh, and some of the species referred to Gymnoptychus Cope. Gymno- 

 ptychus chrysodon is said to lack postorbital processes, which at once excludes 

 it from the Sciuridce, although the genus has been referred by its author to 

 this family, together with Ischyromys Leidy.f 



As the majority of the extinct species of Sciuridai have been described 

 from merely lower-jaw fragments, it is not unlikely that, if they ever become 

 better known, some of the larger genera, as Paramys, Sciuravus, and Gym- 

 noptychus, will be found to embrace species not strictly congeneric ; it being 

 presumable from analogy that species ranging in size from the size of a large 

 Mouse to that of a large Marmot will hardly prove to be referable to the 

 same genera. 



The subjoined account of the extinct forms of Sciuridce is necessarily, 

 from the circumstances of the case, merely a compilation from the original 

 authorities. All that is aimed at is to give a connected synopsis of the sub- 

 ject, embracing the leading characteristics of the described forms, with their 

 localities of occurrence, their approximate size, a notice of the data on which 

 our knowledge of them at present rests, and references to the original papers 

 in which they have been described or noticed. This, owing to the scattered 

 state of the literature of the subject, it has been thought might prove useful 

 to the general student and also to specialists. 



SCIURUS CALYCINUS Cope. 



Sciurus calycinus Cope, Proc. Amer. Pbil. Soc. xii, 1871, 86. 



Described from "two imperfect rami of the lower jaw, with the incisor 

 and first, second, and third inferior molars in situ", found in the Port Ken- 



* Professor Cope refers one species from Colorado, described first as a Paramys, to Sciurus, remark- 

 ing that the remains thus referred do "not differ in any degree from corresponding parts of the existing 

 Squirrels".— {Ann. Rep. U. S. Geol. Surv. Terr! for 1873 (1874), p. 475.) 



t Ibid. p. 474. 



