NATURAL SCIENCES OF PHILADELPHIA. 193 



introduce either genus or species in tlie body of his work, though 

 in the introductory list he gives Synapfomys as a subgenus of 

 Myodes and catalogues a species, S. cooperi. Though defined with 

 precision, as far as the material would allow, the genus remains 

 little known. I can indorse it unequivocally, and add all details 

 hitherto wanting. There is probably no more strongly marked 

 genus of ArvicoUnae. 



The groove of the upper incisor is deep, distinct, and runs near the 

 outer edge instead of along the middle (as in Ochetodon and Reithro- 

 don). The incisors are short, broad, and much curved ; their front 

 much bevelled off, so that, viewed in profile, one part of each incisor 

 stands in front of and parallel with the part on the other side of the 

 groove. These teeth tend to the Myodes pattern further in being 

 enamel tubes not completely filled with dentine (calling to mind 

 an unfinished quill pen, after the first oblique slice is cut away) ; 

 their tips are not straightly transverse, and generally nicked at 

 the end of the groove. The under incisors, exactly as in 3Tyodes, 

 stop as to their roots abruptl^^ just in front and inside of the last 

 lower molar ; while in all other Armcolinse I have examined, ex- 

 cepting Myodes and Cunicuhis^ the root runs past (outside) the 

 lower molar up the ramus of the jaw to near the condyle, this 

 passage of the root making an obvious ridge, here wanting. In 

 Synaplomys, as in the genera just mentioned, the whole condylar 

 ramus is thus flat, with its inner surface nearly plane, separated 

 by a strong sulcus from the end of the alveolar portion of the jaw. 

 , As is well known, the molars of Myodes (restricted to exclude 

 Cuniculus), though essentially aggregated rootless prisms as in 

 other Aroicolinse:, are quite diflferent in their details of pattern. 

 Not to go here into detail, I may simply say, that the inner mar- 

 gin of the molar series is crenate, not sharply serrate like the 

 outer as in Arvicola. Now this pattern of Myodes is duplicated 

 in Synaptomys, and so is every other molar detail. Incisoi's aside, 

 the skull and teeth of Synapfomys are not distinguishable with 

 certaint}^ fi'om those of Myodes. Outside, Synaplomys is not a 

 lemming, but an Arvicola., one, too, with ears as large as in Evo- 

 tomys. An alcoholic specimen might be mistaken at first sight 

 for Arvicola austerus. One might suppose it originally a lem- 

 ming, stranded in time long past in latitude so low as to impress 

 upon it ordinary arvicoline exterior characters. 



