i894. THE LA PLATA MUSEUM. 35 



which he terms E. vectidens, but which, hke the other specimens so- 

 named, I see no reason for separating from E. cni'videns of Owen. 

 Although possessing no complete skulls, like those in the Buenos 

 Aires collection, the La Plata Museum also contains a fine series of 

 the remains of those horses which have been generically separated 

 under the name of Hippidium. Hitherto I have not considered this 

 separation justifiable, but from the study of the actual specimens, I 

 am now convinced that it will be convenient to regard the extreme 

 backward elongation of the nasal slits characterising these extinct 

 horses as a feature of generic value. And here I may mention an 

 instance of that want of appreciation of differences due solely to 

 individual peculiarities and variation in age which unfortunately cha- 

 racterises so much of the palseontological work of Ameghino. On the 

 evidence of a single lower equine molar from the Parana, that gentleman 

 proposed to establish a genus stated to differ from other Equidae by 

 the almost total absence of folds of enamel in the cheek-teeth, for 

 which the name of Hipphapkis was suggested. As a matter of fact, 

 tliis tooth is nothing more than an extremely worn molar of Hippiditim, 

 as is conclusively proved by a large series of Pampean specimens in 

 the Museum, which exhibit a complete transition from the unused to 

 the much- worn type. To make matters worse, when the error was 

 pointed out by Burmeister, the founder of the so-called genus 

 deliberately set to work to justify his own views, instead of frankly 

 acknowledging his error. The existence of a genus closely allied to 

 Equus in the Parana beds, which are set down as of Lower Oligocene 

 age, would not, however, by any means have suited the views of the 

 Argentine palaeontologist, and hence Hipphaplus must be maintained 

 at all hazards ! 



The third genus of South American equines is represented by a 

 very remarkable skull recently discovered in the Pampean deposits 

 on the coast of the province of Buenos Aires, and first described by 

 Dr. Moreno under the name of Onohippidium. While agreeing with 

 the skull of Hippidium in the extreme elongation of the nasal slits, this 

 specimen is distinguished by the presence of an enormous lachrymal 

 fossa of an oblong form and of great depth. Although it is certain 

 this fossa must have contained a large lachrymal gland, its size is 

 much greater than in any other mammal, either living or extinct, 

 with which I am acquainted. The cheek-teeth were of the general 

 type of those of Hippidium. 



{To he continued.) 



R. Lydekker. 



D 2 



