in both families we have long-tailed and short-tailed forms. Cercolabes corresponds to Atherura or Trichys, and Erethizon to Hystrix.
The genus Erethizon, the "Urson" of Canada, has a short, stumpy tail. Its spines are almost hidden by enveloping hair. The fore-feet have four, the hind-feet five toes. The short tail of this creature is remarkable when we reflect upon its climbing habits. It appears, however, to be a weapon with which it strikes sideways at the enemy.
Fig. 244.—Brazilian Tree Porcupine. Sphingurus prehensilis. × 1⁄6.
Of the Neotropical genus Cercolabes (sometimes called Sphingurus, Synetheres, or Coendou) there are some eight or nine species, all found in Central and South America. The animal is arboreal, and has in correspondence with that habit a prehensile tail. The spines are not so stout as in the Ground Porcupines, and are often coloured yellowish or reddish. In correlation with its tree-frequenting habits the bones of Cercolabes show certain differences from those of the Ground Porcupines. The scapula is broader and rounder in front than is that of Hystrix; the phalanges of the thumb (which is rudimentary) are fused together as in the Canadian Erethizon; but those of the very small hallux are also fused, whereas in Erethizon, as in Hystrix, they are separate. In one species, C. insidiosus, Sir W. Flower states that there are as many as seventeen dorsal vertebrae and thirty-six caudals. The tail is thus very long. In C. villosus there are fifteen dorsals and twenty-seven caudals; eight ribs reach the sternum, which is composed of seven pieces, the
