124 O. C. Marsh—New Tertiary Mammals. 
developed. The last upper molar has but a single internal 
these teeth have a strong inner basal ridge. The roof of the 
mouth is deeply excavated between the premolars. The nasals 
are decurved laterally, and much compressed. 
Measurements. 
Extent of upper molar series, - 734° SS 
mettons Of upper true. molara.. 34 es oe 130° 
Antero-posterior diameter of last upper molar, = ee 
Antero-posterior diameter of last upper premolar, -- ----- 28° 
rankeorme Grainieter a 33° 
Space occupied by three right incisors, 75 
Antero-posterior diameter of upper canine at base, ---- -- 2 
Sraneearae Gisitieter oo ee 
Vertical diameter of zygomatic process of squamosal,.... 34 
important parts well preserved. These remains show conclu- 
sively that there are two genera represented among them. One 
of these is doubtless Paleosyops, but the type of that genus 18 
too imperfectly known to determine its more important charac- 
ters. These two genera agree apparently in the structure of the 
anterior portion of the skull, but differ somewhat in their den- 
titi n some specimens, which agree best with Dr. Leidy’s 
original description of Paleosyops paludosus, the last uppeT 
molar has two inner cones, and to this group the name Palo- 
syops may in future be restricted. The other specimens have 
but a single internal cone on the last upper molar, and for the 
genus thus represented the name Limnohyus is proposed. ‘These 
genera may be distinguished from Telmatherium by the pre- 
maxillaries, which are short, stout and depressed, with a small 
median suture. Other distinctive characters of the three genera 
will be given in the full description. 
The present species may be distinguished from those above 
described, especially by the strong basal ridge of the molars. 
