558 U. 8. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



in the middle lower molar, the anterior fifth one of M. 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 refe.ence 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, 1 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 Kichardson's four species, with a fifth from Sitka, described by 

 Wagner as Myodes albigularisf to two, M. torquatus and M. obensis. His synonomy, as relates 

 to our species, is as follows : 



MYODES TORQUATUS. 



JV/us torquatus, PALLAS, N. Sp. Quad. Glirium, 1778, 206. 



Myodes torquatus, KEYS. & BLAS. Enrop. Wirb. 1740, pp. vii and 32. 



MIDDENDORFF, Sibir. Reise, II, u, 1853, 87 ; pi. iv to vii, and x. 

 Mus hudsonius, PALLAS, N. Sp. Quad. Glirium, 1778, 208 

 JMyodes hudsonius, WAGNER, Suf pi. Schreber, III, 1843, 604. 



MIDDENDORFF, Bull. Classe. Math. Phys. Acad Imp. St. Petersb. Ill, xix. 



WIEGMANN'S Archiv, 1845, u, 34. 

 JV/us lenensis, PALL. N. Sp. &c. 1778, 195. 

 Lemmus hudsonius, Sabine, Suppl. App. Parry, 1824, 188. 

 Jrvicola (Gerychus) hudsonia, RICH. F. B. A I, 1829, 132. 

 Gtorychus hudsonius, ABD. & BACH. N. Am. Quad. Ill, 1853, 81 ; pi. cxix. 

 Mus groenlandicus, TRAILL inScoresby's Greenland, 1823, 416. 

 drvicola (Georychus) groenlandicus, RICH. F. B. A. I, 1829, 134. 

 Cuniculus groenlandicus, WAGLER, Isis, 1832, 1220. 

 Mj, odes groenlandicus, WAGNER, Suppl. Schreb. Ill, 1843, 606. 



J. E GRAY, Pr. Zool. Soc. Lend. XVI, 1848, 43. IB. Rae's Narrative, 1850. 

 Georychus groenlandicus, AUD. & BACH. N. A. Quad. Ill, 1854, 315. 

 Lemmus ungulatus, BAER, in Baer & Helmersen Beitrage IV, 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 is in 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 



MiddendorfY, Sibirische Reise, II, n, Wirbelthiere, 1853, 87108. 

 Wagner, Suppl. Schreber's Saugethiere, III, 1843, 602. 



