28 
THE GEOLOGIST. 
Geog. Distrib. Taguatagua lagoon {Gay). — Geol. Age. Pliocene. 
Eqtjus nearcticus. — Syn. Equus Americanus (Leides). 
Characters ? — I am yet unable to form any distinct idea as to this species from the 
few figures and descriptions 1 have seen. The name Aniericanus is, however, glaringly 
inappropriate ; as also, in a less degree, are those of E. neogaus (which should be neo- 
tropicus), and Chileiisis (a name which the discovery of the species elsewhere would 
nullify). Names like curvidens, plicidens, macrognathus, are much more convenient, as 
they give a more or less distinct idea of the characters of the fossil. 
Geog. Distrib. Confederate and Federal States. — Geol. Age. Plio- 
cene. 
The problem whicli we have to solve is, whether the E. Cliilensis, 
neogcBiiSy and curvidens are distinct species. Grervais, in Castelnau's 
work (page 33), assigns them all to one species, of which he retains 
the name JE. neogceus. He however separates E. Devillii with an 
expression of donbt, saying that " slight differences in the form of 
lower molars, and a smaller size than that of E^uus neogceus, are 
the only characters which we can yet assign to it. Its smaller 
size seems to exclude the possibility of its similitude with E. princi- 
]palis, of which the undiagnosticated name appears to indicate a cer- 
tain superiority in relation to the other animals of the same genus." 
The fragment of lower jaw belonging to E. Devillii bore the six 
principal molars. These teeth are small, with less coronal complexity, 
and remarkable for a little different disposition of the houcles internes 
which the enamel forms inside each lobe. The total length of the six 
molars is only 0"160, instead of 0*195 ; the first tooth, separately, 
measures 0-030, instead of 0*035, in the E. neogceus ; the fourth, 0*024, 
and the sixth, 0 030. I cannot coincide with M. Gervais in con- 
sidering these differences specific. 
The question, whether Chilensis and neogceus are identical, next 
comes before one. In order that my readers will appreciate tlie diffi- 
culty, I figure 76 from G-ay's 8th plate, and 4 a from Castelnau's 7th 
plate. The first is E. Chilensis, the second E. neogceus. 
E. curvidens (Owen) I am unable specifically to distinguish from 
E. neogceus. I figure the corresponding teeth. 
The object of this brief note is merely to point out that the time 
is not yet arrived when any general proposition can be laid down 
respecting the geographical distribution of horses in the ]N"ew World. 
As regards their geological age, they are all from later tertiary, pro- 
bably pliocene or pleistocene deposits. Is' one of the South American 
species ofter any points of resemblance to the genus Hipparion, or 
three-toed horse of the Old World. No species of Hipparion has yet 
been discovered in America. 
ExPLANATICfN OF THE PlATES. 
PI. II. Fig. 3, Equus macrognathus ; fig. 4, Equus Devillii. 
PI. III. Fig. \, Eq7(us Chilensis ; fig. 2, Equus macrognathus ; fig. 3, Equus macro- 
cephaltcs. 
