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32 



MONOORAl'IIS OF NORTH AMKKIOAN UODBNTIA. 



tened nail. Hind feet very long, generally about equali .^ distance from nose 

 to ear; 1st and 5tli toes subequal and very short, the latter reaching but little 

 beyond the basal joint of the 4th. Soles entirely nailed, granular at bases 

 of toes, perfectly smooth i)ehind, G-tul)ercnlate, the tubercles all small, the 

 hindcrmost not lengthened and linear as in Mux; the 2d tubercle just outside 

 and a little in advance of this one; a tubercle just inside the base of the 1st 

 and 5tii toos respectively ; one between bases of 2tl and Ikl toes ; one between 

 bases of 3d and 4th toes. 



Although this forni of sigmodont Murina is undoubtedly strongly marked, 

 yet we cannot see that it stands apart from the rest so far as it is tacitly sup- 

 posed to. A good deal that has been written about its peculiarities of denti- 

 tion might be advantageously toned down ; in fact, we do not find much, if 

 any, greater dental characteristics than those slightly superspecific ones mark- 

 ing several other forms usually ranked as subgenera of Hesperomys. The 

 loops of enamel on the posterior molars tlo form a sort of sigma, but it is 

 usually a broken and always a distorted one, never more evident than in some 

 other sigmodont forms. The pattern of the teeth is fully as changeable with 

 age as it is in Hesperomi/s, Scotoma, Mus, and other genera; and it is only to 

 a particular stage of the crowns that the details of pattern, usually ascribed to 

 the genus, hold good. Moreover, we have, in the section Oryzomys, a perfect 

 link between Sigmodon and the ordinary small Hesperomys of America. The 

 connection is so close and complete, that, in fact, we should almost think Ory- 

 zomys ought to take |)lace as a sui)genus of Sigmodon rather than of Hespero- 

 mys; or, if retained where it is now, Sigmodon ought to be laid over against 

 it as another suljgcnus of Hesperomys. In external characters, Oryzomys 

 agrees better with Sigmodon than it does with ordinary Hesperomys ; the two 

 are so much alike, in fivct, that the relative length of the toes and the com- 

 parative size of the ears are the most readily-expressed differences. We are 

 not sufficiently familiar with all the exotic American Murinee to come to a 

 final conclusion : but we suspect that it will in time be found advisable or 

 necessary to combine most of the species of the sigmodont Mures into one 

 genus (for which the name Sigmodon, antedating Hesperomys, woulil have to 

 be adoi)ted), with several subgenera or groups of species; for, with the 

 exception of Neutoma, perhaps Holochilus, and possibly one or two others, 

 the various superspecific groups seem to differ from each other by characters 

 of ai)out ecpial or equivalent value. The impropriety is, that it is at present 

 customary to hold some of these groups fur genera, others only for subgenera ; 



