68 GEOLOGICAL SURVEY OF TEXAS. 



so as to be connected by a narrow anteroposterior isthmus, and separated 

 on the internal face of the crown by a wide channel which has a greater 

 anteroposterior diameter than the metaconid and metastylid respectively 

 near the apex of the crown, and an equal width at the base of the crown. 

 The hypostylid is also appressed to the hypoconid and has a recurved 

 posterointernal angle, which forms an acute ridge bounding the internal 

 face of the crown posteriorly. Tliis incloses with the metastylid a flat 

 open gutter as wide as the metastylid. A sharp ridge marks the internal 

 face of the anterior border, but it is closely appressed to the metaconid, 

 which it does not equal in elevation. 



Measurements. 



Mm. 



Length of crown preserved 37 



Anteroposterior diameter at middle 16.5 



Transverse diameter at metastylid S 



Transverse diameter in front of metastylid 6 



This species differs widely from any horse in the characters of its infe- 

 rior molar. Besides the flattening and anteroposterior extent of the 

 metaconid-metastylid, it is peculiar in the large size and internal flatten- 

 ing of the hypostylid. It is this flattening which causes the wide flat 

 channel of the internal face, which equals in width that between the met- 

 aconid and metastylid, and is more sharply defined. The Equus minutus 

 is also the smallest known species of true horse, as its teeth do not exceed 

 in size those of a sheep. 



PLATYGONUS, Leconte. 



The species of this genus have been hitherto found in the cave forma- 

 tion of the Eastern States and Pleistocene deposits of Mexico (Duges). 

 It is therefore of interest to find it in the older horizon of the Blanco. 



PLATYGONUS BICALCAEATUS, CopC. 



Sp. nov. Plate XIII, Figure 5. 



The remains of this species which have been obtained so far include 

 only portions of the last inferior molar, and the superior canine which 

 lacks most of the crown, and which were found together, and an inferior 

 canine found at another place. These specimens display distinctive char- 

 acters, and as they indicate an important peculiarity of the Blanco fauna, 

 it is necessary to describe them. 



The inferior molar lacks the anterior crest. The posterior crest and 

 heel display characters that distinguish it from the corresponding parts 

 of the P. compressus. The talon consists of two principal cusps, which 

 are connected by a cross-crest, as is the case with the other cusps of th? 



