MESOZOIC FOSSILS. 609 



ECHINOIDEA. 



Fragmentary casts of one or more species of echinoids were obtained 

 near the lower canyon of the Yellowstone River and at a locality north of 

 Berry Creek, a tributary of Snake River. They are doubtless new species, 

 but they are not sufficiently well preserved for generic determination, and 

 we must therefore wait for additional and better material. 



BRACHIOPODA. 



Rhynchonella myrina Hall and Whitfield. 



Rhynchonella myrina Hall and Whitfield, 1S77 : IT. S. Geol. Expl. 40th Parallel, Vol. 

 IY, Pt. II, p. 284, PI. VII, figs. 1-5. Whitfield, 1SS0 : Geol. Black Hills Dakota, 

 p. 347, PI. Ill, fig. 6, not fig. 7. 



The type of this species is a finely plicate shell with about eight plica- 

 tions in the median sinus. In Prof. R. P. Whitfield's later publication he 

 has united with it the much more coarsely plicate forms, with only three or 

 four plications in the median sinus, that have usually been referred to JR. 

 gnathophora. As the numerous specimens in the present collection do not 

 show the intermediate varieties of form and sculpture, I prefer to treat them 

 as distinct species. 



Typical JR. myrina occurs at a number of localities in the northwest 

 corner of the Park and near Snake River southwest of it, in the hard 

 arenaceous limestone. 



Rhynchonella gnathophora Meek. 



PI. LXXII, figs. 1-4. 



Rhynchonella gnathophora Meek, 1S04: Geol. Surv. California, Palseont., Vol. I, p. 39, 



PI. VIII, figs. la-/. 

 Rhynchonella gnathophora % Hall and Whitfield, 1877: U. S. Geol. Expl. 40th Parallel, 



Vol. IV, Pt. II, p. 2S4, PI. VII, fig. 0. 

 Rhynchonella myrina (H. and W.) Whitfield, 1880: Geol. Black Hills Dakota, p. 347, 



PL III, flg. 7, not fig. 6. 

 Rhynchonella. sp. Meek aud Haydeu, 1865: Pakeont. Upper Missouri, p. 71, PL III, 



fig. 4. 



The specimens referred to this species have nearly the same outlines 

 as JR. myriyia, but they are somewhat more capacious and much more coarsely 

 plicate. The type of R. myrina has thirty plications on each valve, with 



MON XXXII, PT II 39 



