FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 251 



Simpson: Closely resembling Edocion, but upper premolars with 

 much smaller metacones, first and second molars with slightly smaller 

 mesostyles and hypocones, protoconules of P^~* and M^"^ slightly 

 more united by lophs to protocone. 



Discussion. — The molars of this genus can hardly be distinguished 

 generically from Edocion, although unlike any known species in 

 details. The prem^olars, however, are distinctly less molariform and 

 at once distinguish Gidleyina from Edocion. It is well known that 

 from partial dentitions alone it is often difficult or impossible to 

 determine even the ordinal affinities of genera in these ancient faunas, 

 but in this case every indication is that Gidleyina is in fact related to 

 Edocion, and perhaps ancestral to it." 



If this is correct, it is clear that the Edocion line was already distinct 

 from that of Phenacodus in the Middle Paleocene and had already 

 acquired a mesostyle and slightly more lophiodont pattern, although in 

 other respects, such as the complication of the premolars, not more 

 advanced than Tetraclaenodon}^ 



Among Torrejon genera, Gidleyina most closely resembles Pro- 

 toselene in many respects but is at once distinguished by the large and 

 posterointernal protocone on P^, distinct conules on P*, and other lesser 

 details, suggesting that the relationship is not very close. The dis- 

 tinctions from Protoselene are resemblances to Edocion. 



In addition to the type, based on an upper jaw, I tentatively 

 refer two species based on lower jaws to this genus. They are 

 described below. 



GIDLEYINA MONTANENSIS (Gidley) 



Figure 72 



Gidleyina montanensis (Gidley) Simpson, 1935d, p. 240. 



Type. — Princeton no. 12048, part of left maxilla with P^-M^ and a 

 probably associated right P^. 



Horizon and locality. — Loc. 68, about 1,000 feet above Gidley 

 Quarry, Fort Union, Sweetgrass County, Mont.^^ 



»i This is Dr. Qidley's opinion in all three drafts of the manuscript on this form, but still later he noted 

 that affinity is closer with Protogonodon. This seems to me highly improbable and was perhaps noted 

 rather as a point to check than as a conclusion. 



" In one of his manuscripts Dr. Gidley proposed placing the Tetradaenodon-Phenacodus and the Gidleyina- 

 Eciocion phyla in different subfamilies. Even if we grant that the phyla were distinct from Middle Paleo- 

 cene to lower Eocene, they are so similar that considering them as two subfamilies seems to me dispropor- 

 tionate to the classification of other groups of mammals. 



" There are now no locality data with the specimen. One of Dr. Gidley's manuscripts says "Near sec. 

 23, R. 15 E., T. 5 N. . . near top of Fort Union No. 2 of Silberling." Localities 4, 52, and 54 are the only 

 ones in (or near) this section— the Gidley Quarry and a nearby exposure near the same level. As far as I 

 can determine, no Princeton material came from anywhere near here. Another of Dr. Gidley's drafts, and 

 apparently the latest, says "From the vicinity of Bear Butte. . . . Exact level not known, but probably 

 from near the middle of the section of this locality." Mr. Silberling, however, remembers the discovery 

 of the specimen and positively states that it was found at the locality now numbered 68. Two other speci- 

 mens perhaps of this species are from the cluster of localities in the western part of T. 5 N., R. 15 E., where 

 most of the Princeton specimens were found, some 1,500 feet above the base of No. 3. 



