304 



TITANOTHERES OF ANCIENT "WYOMING, DAEIOTA, AND NEBRASKA 



the front, and is set on the outer side of the line of the 

 grinders. 



Dentition: In the superior teeth we note especially 

 that (1) m^ is small; (2) the crested metaconules are 

 confluent internally with the hypocone; (3) the 

 parastyle is elongated on the outer side of the ectoloph 

 and somewhat more sharply ridged; (4) the ectolophs 

 of premolars have more sharply defined convex ridges 

 opposite the paraconules and metaconules; (5) the 

 hypoconulid of ms is rather sharp and prominent, 

 laterally depressed, and very slightly crescentic. 



Measurements of species of Limnohyops, in millimeters 



• Estimated. 



The distinctions in measurement and proportion 

 noted above are based upon our present loiowledge 

 and are by no means so full and definite as we should 

 wish. 



Comparison of the species. — The known species of 

 Limnohyops do not form a progressive phyletic series 

 in the ascending geologic scale, whereas the known 

 species of Palaeosyops form a finely progressive 

 phyletic series. 



The type of L. (Palaeosyops) laevidens Cope, from 

 Bridger B 1-2, is a relatively small and primitive 

 form, an undoubted Limnohyops in skull structure, 

 distinguished by a small p^ of rounded form. All 

 the teeth in the type are greatly worn. 



Considered in ascending geologic order from Bridger 

 B 1 to D the species may be distinguished as follows: 

 The type of L. priscus Osborn is recorded as from the 

 same geologic horizon — namely, Bridger B 2 — but it 

 is an animal of greater size and has a p^ of elongate, 

 triangular form. 



The large and heavy type of L. monoeonus Osborn 

 also occurs in Bridger B at Grizzly Buttes. It is 

 named the "single-coned species" in reference to the 

 absence of the hypocone on m'. Except in this 

 character it is a typical Limnohyops. 



The type of L. matthewi also occurs in Bridger B 2, 

 a surprising fact because of its extremely short and 

 broad skull proportions. It exhibits the extreme of 

 brachycrany. 



L. laticeps, the type species of the genus, occurs 

 much higher up — namely, in Bridger C and D. It is 

 less specialized in skull structure than L. matthewi 

 and has the generic character of the presence of the 

 hypocone on m^ very marked. 



QXTANTITATIVE EVOIUTION OF IIMNOHYOPS 



The accompanying table gives the measurements of 

 29 characters of proportion in 11 specimens, repre- 

 senting 5 species, collected at ascending geologic levels 

 in the Bridger formation. 



Evolution of proportions of Limnohyops 



[Measurements in millimeters] 



