(310 GEOLOGY OF THE YELLOWSTONE NATIONAL PABK. 



eight in the median sinus, while the plications on these shells vary from 

 fourteen to twenty, with three or four in the median sinus, three being- 

 much the more common number. A few specimens have only two. 



I have not seen Meek's types from the Jurassic of California, but 

 specimens from the Mormon sandstone near Taylorsville (probably Meek's 

 original locality) have been kindly loaned by Professor Hyatt for com- 

 parison. These are larger than any of the Utah or Yellowstone specimens, 

 and none of them has less than four plications in the median sinus, but in 

 all other respects they agree quite closely. All the figured specimens from 

 the Black Hills and Rocky Mountain region above referred to have been 

 examined, and I have no doubt of their specific identity. In Yellowstone 

 National Park, where the species is very abundant in the upper zone of the 

 Jurassic and occasionally occurs in the underlying shales, the specimens are 

 usually small, many of them being no larger than the one from the Black 

 Hills figured by Meek and Hayden. 



It is known from northwestern Colorado and from the Uinta Moun- 

 tains, Utah, and it occurs in the Park near the northern and Lake heads of 

 Fawn Creek; on south slope of ridge south of Gray Mountain; south side 

 of Fan Creek Pass; on saddle at head of Fawn Creek, northeast of Monu- 

 ment Peak, in beds 100 feet above principal fossiliferous horizon of Jurassic; 

 in saddle west of south head of Gardiner; 4 miles north of second crossing 

 of Snake River, at 7,500 feet elevation; on hill northeast of Mount Everts; 

 on ridge south base of northwest slope of Flat Mountain; at Mammoth 

 Hot Springs, on main terrace. 



PELECYPODA. 



OSTREA STRIGILECULA White. 



Ostrea strigilecula White, 1875 : U. S. Geog. and Geol. Surv. W. 100th Meridian, Vol. 

 IV, Pt. I, p. 103, PI. XIII, figs. 3a-d. 1884: Fourth Ami. Kept. U. S. Geol. 

 Surv., p. 289, PI. XXXV, figs. 9-11. Whitfield, 1880: Geol. Black Hills Dakota, 

 p. 318, PI. Ill, figs. S-12. 



Specimens referable to this small and somewhat obscure species were 

 collected from almost every locality with Bhynchonella f/nathophora and on 

 northeast spur of peak west of mouth of Coulter Creek; west end of ridge 

 southeast of Mink Creek; Mount Sheridan; lower limestone on Fawn 

 Creek plateau; east end of northeast spur from Signal Peak; saddle in 

 ridae west of south head of Gardiner. 



