Synaptomys borealis (Richardson, 1828)

Species diagnosis

General Characteristics

• Cheek teeth longitudinally simplified (few loops)
• Inner salient angles of upper molars and outer angles of lower molars smaller than those of the opposite sides
• m1 with 3 closed triangles between termination loops (or with traverse loops if close triangles absent)
• Supraorbital ridges fusing in adults, forming median orbital crest
• Posterior palate not terminating as a simple transverse shelf
• Upper incisors strongly grooved
• Tooth rows not, or not widely divergent posteriorly

Alaska subspecies