Incisors two in each jaw, large, and strong, remote from the grinders: tusks none: toes distinct, with small conical claws.

* Furnished with strong clavicles.

14. Sciurus

Grinders simple, with tubercular summits, five above and four below on each side: upper incisors chisel-shaped; lower ones pointed, compressed laterally: toes long, armed with sharp claws: tail long and bushy.

15. Myoxus

Grinders simple, their summits marked with transverse ridges of enamel, four on each side above and below: hair very soft and fine: tail very long, somewhat bushy.

16. Mus

Grinders simple, with tubercular summits, three on each side above and below: upper incisors wedge-shaped, lower ones compressed and pointed: tail nearly naked, annulated with scales.

17. Arvicola

Grinders compound, with flat summits, the enamel appearing in ridges on the surface : upper incisors chisel-shaped, lower ones pointed: tail round and hairy, shorter than the body.

18. Castor

Grinders compound, with flat summits, four on each side above and below: toes of the hinder feet palmated: tail oval, depressed, and covered with scales.

** Clavicles rudimentary.

19. Lepus

Two subsidiary incisors in the upper jaw immediately behind the others: grinders six above and five below on each side, the summits flat, with transverse plates of enamel: inside of the cheeks hairy: ears very large: toes five before and four behind i tail short, and turned up.

20. Cavia

Grinders compound; each with one simple and one fork-shaped plate of enamel; four on each side above and below: toes four before and three behind: tail none.