558 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
in the middle lower molar, the anterior fifth one of MZ. lemmus and schisticolor being deficient. 
Neither of these last species has anything like the conspicuous groove on the extero-anterior face 
of the upper incisors. 
The differences from Arvicola are too great to need special expression. The four prisms of 
the posterior lower molar and the five of the anterior are all sufficient as characteristics. 
Although there are not the means at hand to characterize this animal perfectly, either 
generally or specifically, yet its peculiarities are such as to render it not improper to give it a 
place in the zoological system by calling it Synaptomys, (S. cooperi,) in reference to the close 
connexion it exhibits of the characters of Arvicola and Myodes. 
I have already stated that no specimens of true Myodes from North America have fallen under 
my examination. For the sake of completing the account of the North American mammals, I 
propose to introduce brief diagnoses of the species described by authors. According to Midden- 
dorff,! who has had unequalled opportunities of investigating this genus in its native localities, 
many nominal species have been introduced into the system by describing the Old and New 
World Lemmings as distinct, when, in reality, they are the same ; and this author finds a further 
source of error in the fact that the very different coloration of varying age, sex, and season, so 
little understood before the publication of his paper, has been made the basis of other nominal 
species. Middendorff reduces Richardson’s four species, with a fifth from Sitka, described by 
Wagner as Myodes albigularis,? to two, M. torquatus and J. obensis. His synonomy, as relates 
to our species, is as follows: 
MyYopdEs TORQUATUS. 
Mus torquatus, Patias, N. Sp. Quad. Glirium, 1778, 206. 
Myodes torquatus, Keys. & Bias. Europ. Wirb. 1740, pp. vii and 32. 
Mippenporrr, Sibir. Reise, II, 1, 1853, 87; pl. iv to vii, and x. 
Mus hudsonius, Partas, N. Sp. Quad. Glirium, 1778, 208 
Myodes hudsonius, Wacner, Suppl. Schreber, III, 1843, 604. 
MippenporrF, Bull. Classe. Math. Phys. Acad. Imp. St. Petersb. III, xix. 
Wiecmann’s Archiv, 1845, n, 34. 
Mus lenensis, Pari. N. Sp. &c. 1778, 195. 
Lemmus hudsonius, Sabine, Suppl. App. Parry, 1824, 188. 
Arvicola (Gerychus) hudsonia, Ricn. F. B. A I, 1829, 132. 
Georychus hudsonius, Aup. & Bacu. N. Am. Quad. III, 1853, 81; pl. cxix. 
Mus groenlandicus, TRrat.u in Scoresby’s Greenland, 1823, 416. 
Arvicola (Georychus) groenlandicus, Ricu. F. B. A. I, 1829, 134. 
Cuniculus groenlandicus, WAGLER, Isis, 1832, 1220. 
Myodes groenlandicus, Wacner, Suppl. Schreb. III, 1843, 606. 
J. E. Gray, Pr. Zool. Soc. Lond. XVI, 1848, 43.—Is. Rae’s Narrative, 1850. 
Georychus groenlandicus, Aup. & Bacu. N. A. Quad. III, 1854, 315. 
Lemmus ungulatus, Barr, in Baer & Helmersen Beitrige 1V, 1841, 283. 
From the preceding list it will be seen that Middendorff makes Myodes hudsonius and groen- 
landicus synonyms of torquatus. The peculiarity of hudsonius isin having the two middle fore 
claws very large, much compressed, the extremities blunt, and divided by a terminal notch 
into two points, one above the other. This, however, has been observed in Asiatic specimens to 
a still greater degree than in American, giving rise to the Lemmus ungulatus of Baer. 
There seems no good reason to contest the decision of Middendorff in regard to the species, 
as he examined all the English specimens upon which the descriptions of Richardson, Audubon 
and Bachman, and others, quoted above, are based. His article is very full, describing and 
Middendorff, Sibirische Reise, II, 1, Wirbelthiere, 1853, 87—108. 
Wagner, Suppl. Schreber’s Siugethiere, III, 1843, 602. 
