The comparative morphology and biometry of the lower cheek teeth of modern Equus are studied on approximately 300 mandibles belonging to the 10 usually recognised species : Equus grevyi, E. burchelli, E. quagga, E. zebra, E. africanus, E. asinus, E. hemionus, E. klang, E. przewalskii, E. caballus. The studied parameters comprise : occlusal length and width, postflexid length and index ; shape of the double knot (metaconid + metastylid + lingual groove) ; depth of the vestibular groove on the molars ; frequency of the pli caballinid, protostylid and other enamel plications or islets ; frequency of the dP/l.
The same methods of study are applied to a number of North American, Eurasian and African species. For the sake of comparison, some Hemphillian equids were observed (Dinohippus interpolatus, Dinohippus leidyanus, Astrohippus ansae, Phiohippus mexicanus) but most of the discussed material belongs to Pliocene or Pleistocene species of Equus : the « stenonine ›› E. stenonis, E. simplicidens, E. sanmeniensis and E. teilhardi; the « caballine ›› E. scotti, E. lambei, E. Iaurentius, E. mosbachensis, E. germanicus, E. gallicus, E. taubachensis and the Liakhov horse. The relationships of other species, in particular the North American E. calobatus, E. occidentalis, E. cf mexicanus are not clear for the moment. ln Africa, the Plio-Pleistocene species from Koobi Fora (Kenya) show some stenonine and perhaps asinine affinities. The relationships of E. numidicus and E. tabeti are uncertain but these species are probably related to the East African ones. E. mauritanicus is most certainly related to the Quagga group.
The biometrical data are gathered in 32 tables ; 4 photographie plates and 19 figures illustrate the next. The whole is a complement of the previously published studies of the skulls, upper cheek teeth, incisors and metapodials of modern and fossil Equus.

  

The biometric and morphologie variability of the cheek teeth in the end-of-the-phylum species Lophiodon lautricense Noulet studied in this note, reposes on the observation of about 800 teeth. These were revealed to be little variable in absolute dimensions. The considerable morphologie variability in the upper premolars permitted the problem of the molarization process to be taken up. An hypothesis concerning the order of eruption of the cheek teeth is formulated based on an examination of a large number of milk dentitions. In conclusion, it is suggested that reservations be held on the value of dental characters classically used in systematics for the group under consideration.