MURIDA—SIGMODONTES—H. LEUCOPUS GOSSYPINUS. On 
ranking nearly with sonoriensis as to the degree of geographical differentiation 
that it has sustained. 
The propriety of this step will appear in still stronger light after exam- 
ination of the so-called ‘‘ Hesperomys cognatus” of LeConte and Baird, which 
we are now prepared to discuss. Apart from the published accounts of the 
two authors just named, our material is, first, three dried specimens, labeled 
“‘cognatus” in what we presume to be Major LeConte’s own handwriting, as 
it is the same as that upon his other types now in our possession ; secondly, 
five dried and several alcoholic specimens referred to this species by Baird, 2. ¢. 
The latter will be first noticed. 
Two of these, Nos. 673 and $05, from North and South Carolina, respect- 
ively, are precisely like /ewcopus in every respect, except that the tails of both 
are much less distinctly bicolor than usual in dewcopus. Out of our series, 
however, of unquestioned and unquestionable deucopus, we can precisely match 
this feature. The other three specimens are from Mississippi (Nos. 562, 583, 
586). They are all in wretched condition, having been skinned out of alco- 
hol. One of them, 562, is not half grown (body, 2.25; tail, 1.42, &e.); it is 
dark lead-color, and from the shortness of the tail represents sonoriensis, if 
anything different from /eucopus. The second is nearly grown, but still in the 
mouse-gray pelage; the tail is 2.50 to a body of 3.00, and therefore not shorter 
in proportion than in /ewcopus; and the tail is very sharply bicolor. The third 
appears grown, but the colors are indeterminable, from immersion in alcohol 
and from loss of most of the fur; the tail is plainly bicolor; the proportions 
are just as in an average of /cwcopus. We must confess that, even if there 
were a species “cognatus” distinct from leucopus, we do not see how these 
five specimens could be taken to represent it. Much as we regret our decision, 
we must say that they are all unquestionably Zewcopus. 
The remaining specimens (alcoholic) we cannot distinguish even as a 
tangible variety of leucopus. 
Major LeConte’s types do not seem to have been in Professor Baird’s 
hands when the article on the Mammals of North America was being pre- 
pared; and the latter had to guess at the former’s meaning—a difficult matter 
indeed, since Major LeConte’s description amounts to exactly nothing. Of 
his three specimens, one of them (from Illinois), we find to our great surprise, 
is an example of H. michiganensis, pure and simple! (Head and body, 2.90; 
tail, 1.90, sharply bicolor; hind foot, 0.66; &c.) The other two, Nos. 4708, 
