"Grattius, too, writes that "great glory exalts the far-distant Celtic dogs" and refers to the Vertragus, an ancestor of the modern greyhound. "Swifter than thought or a winged bird it runs, pressing hard on the beasts it has found" (204ff).
Arrian has much to say about the dog in the Cynegeticus, written in Greek about AD 150 as a supplement to the manual of Xenophon. Arrian suggests that Xenophon must not have known of the Vetragus, which was named for its swiftness; otherwise, he never would have written that a hound cannot catch a hare except by luck. If the Vertragus does not run down the hare, it must be because of broken ground or a concealing thicket or ditch. A hare startled too close will not even have a chance to run at all.
"Splendid animals, the best bred of them, with fine eyes, fine bodies all over, fine coats, and fine appearance" (III.7), they should be long from head to tail, with a sturdy build, a muzzle that comes to a point, and large soft ears. The eyes should be prominent, large and bright and "should astonish the man who sees them" (IV.5). Again, he corrects Xenophon: "The color makes no difference, whatever it may be, not even if hounds are black or tan or white all over" (VI.1)."
(from http://penelope.uchicago.edu/~grout/encyclopaedia_romana/miscellanea/canes/canes.html )
Now here was I thinking that the Large Soft Ears were just him! Not that he would catch a hare, but mostly because he agrees with Arrian : " "For one does not take hounds out in order to catch the beast, but for a race and competition, at least if one is a true sportsman."