FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 59 



following from Loc. 24 (immediately above the mammals): Viviparus 

 retusus, V. planolatere, and Lioplax nebrascensis; and the following 

 from Loc. 67, high in the No. 3: INedionidus senectus, IN. s. declivis 

 (type locality; Russell, 1934), Viviparus retusus, and V. cf. planolatere. 



(There are also large collections not adequately studied, nor is it 

 necessary to discuss them here where only the general ecological 

 aspect is in question.) 



Altogether, the invertebrates show that fresh water was abundantly 

 present and thickly populated in this area throughout the deposition 

 of the Fort Union. 



Fishes. — Fish remains are abundant in the field but usually very 

 fragmentary. A few relatively good specimens have been recovered 

 but have not yet been prepared or closely studied. Gar scales (Lep- 

 isosteus sp.) are common at most surface localities and also occur in 

 all three quarries. A stUl commoner fish in the quarries, seldom 

 found on siu-face exposures, probably because of its more fragile 

 character, appears to be an ally of, or to belong to, Stylomyleodon 

 Russell, and Russell has already recorded its presence in this field 

 (1928, p. 107). Specimens recently collected will add greatly to 

 knowledge of this form. Despite the almost complete lack of associa- 

 tion of mammal remains in the Gidley Quarry, it is the rule rather 

 than the exception to find fishes, apparently mostly Stylomyleodon, 

 represented by associated strings of vertebrae, despite the loose 

 articulation of these, and not infrequently also with parts of the skull 

 in association. 



Reptiles. — Champsosaur and crocodilian remains, generally too 

 imperfect for close identification, are common at all levels. Isolated 

 teeth suggest that Allognathosuchus was the common crocodilian. 

 Champsosaurs occur up to at least 3,000 feet, and possibly more, 

 above the base of the No. 3. Turtle remains are also common, but 

 they also are usually too fragmentary for ready identification. Hay 

 (1908, p. 498) has, however, described Aspideretes nassau from a 

 specimen found by one of the Princeton parties in the No. 3 beds. 



Gilmore (1928b) has mentioned three fragmentary specimens of 

 Peltosaurus sp. from the Fort Union No. 2 Silberling Quarry and has 

 also named Harpagosaurus excedens, the type of which is from the 

 same locality. Lizard remains are fairly common in both Silberling 

 and Gidley Quarries, and it is probable that these animals were 

 abundant in this region in the Middle Paleocene. 



MAMMALIAN FACIES 



The percentage composition of the principal No. 2 surface locali- 

 ties, all near the same level and similar in facies, and of each of the 

 three quarries is given in table 4 and shown graphically in figures 

 1 and 2. 



