23 



T1IE GEOLOGIST. 



Geog. Distrih. Taguatagua lagoon (Gay). — Geol. Age. Pliocene. 



Eqtjtjs nearcticus. — Sgn./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 Americanus is, however, glaringly 

 inappropriate; as also, in a less degree, are those of E. neogceus (which should be neo- 

 tropicus), and Chilensis (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. Distrih . Confederate and Federal States. — Geol. Age. Plio- 

 cene. 



The problem which we have to solve is, whether the E. Chilensis, 

 neogceus, and curvidens are distinct species. Grervais, in Castelnan'3 

 work (page 33), assigns them all to one species, of which he retains 

 the name E. neogceus. He however separates E. Devillii with an 

 expression of doubt, saying that " slight differences in the form of 

 lower molars, and a smaller size than that of Eqiius 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 boucles internes 

 which the enamel forms inside each lobe. The total length of the six 

 molars is only 0*160, instead of 0195 ; 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 the diffi- 

 culty, I figure 76 from Gray'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 New World. 

 As regards their geological age, they are all from later tertiary, pro- 

 bably pliocene or pleistocene deposits. None of the South American 

 species offer any points of resemblance to the genus H.ipparion, or 

 three-toed horse of the Old World. No species of Hipparion has yet 

 been discovered in America. 



Explanation of the Plates. 

 PI. II. Pig. 3, Equus macrognathus ; fig. 4, Equus Devillii. 



PL III. Fig. 1, Equus Chilensis; fig. 2, Equus macrognatlius ; fig. 3, Equus macro- 

 cephalus. 



