SCIURIDZH—EXTINCT SPECIES. 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 Sciuride, 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 Sciwrus hudsonius to those one-fourth larger 
than Arctomys monax. Other apparently Sciurine forms are the genera Tazx- 
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 Sciurzde, although the genus has been referred by its author to 
this family, together with Ischyromys Leidy.t 
As the majority of the extinct species of Sciwrid@ 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 Sciurid@ 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 Core, Proc. Amer. Phil. Soc. xii, 1871, 86. 
Described from ‘“‘two imperfect rami of the lower jaw, with the incisor 
and first, second, and third inferior molars zz 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. 
