MESOZOIC FOSSILS. 613 



Lima cinnabarensis is distinguished by its simple equal ribs. It has more 

 resemblance to the Cretaceous Lima utahensis of the Colorado formation. 



Locality: Cinnabar Mountain, Montana, where it is associated with 

 Pleuromya subcompressa, Plioladomya kingi, Trigotiia montanaensis, etc. 



Genus CAMPTONECTES (Agassiz) Meek. 



Shells belonging to this genus are very abundant in the Jurassic of 

 the Rocky Mountain region. In Yellowstone National Park almost every 

 Jurassic locality has yielded specimens, but in many cases they are frag- 

 mentary or mere casts that can not be assigned to species with any con- 

 fidence. Five American Jurassic species have been described, of which 

 three at least are sufficiently well characterized to be easily distinguished 

 when good specimens are examined. These are Camptonectes bellistriatus 

 (to which a new variety is added below), C. platessiformis, and C. stygius. 



The types of 0. extenuatus are casts in sandstone that show neither 

 sculpture nor the forms of the ears. It may be a distinct species, but it is 

 more probable that it is either the young of C. bellistriatus or the form after- 

 wards named C. pertenuistriatus by Hall and Whitfield. I do not feel quite 

 certain that the latter is distinct from C. bellistriatus, young specimens of 

 which when slightly exfoliated would be very similar; but in the present 

 collection there are many specimens that can be most conveniently referred 

 to C. pertenuistriatm, and the name is therefore retained. All of the species 

 mentioned excepting C. stygius are represented in these collections. 



Camptonectes bellistriatus Meek. 



PI. LXXII, fig. 12. 



Pecten bellistriata Meek, 1860: Proc. Acad. Nat. Sci. Phila., p. 311. 



Camptonectes bellistriatus Meek and Hayden, 1865: Pakeout. Upper Missouri, p. 77, 



figs. A-D. Meek, 1876: Simpson's Rept. Expl. Great Basin, Utah, p. 356, PI. 



Ill, figs. 3a-cl. Hall and Whitfield, 1877 : Eept. U. S. Geol. Expl. 40th Parallel, 



Vol. IV, Pt, II, p. 289, PI. VII, fig. 13. Whitfield, 18S0: Geol. Black Hills 



Dakota, p. 351, PI. IV, figs. 6-11. 

 1 Camptonectes extenuatus (M. and H.) Hall and Whitfield, 1877 : Eept. U. S. Geol. 



Expl. 40th Parallel, Vol. IV, Pt. II, p. 290, PI. VII, fig. IS. 

 Imperfect specimens that appear from general form and details of 

 sculpture to agree with this well-known species were collected at head of 

 Fawn Creek, upper bed; divide between Fawn Creek and Gallatin Valley; 



