JURASSIC FOSSILS. , 345 



The species appears to have been somewhat abundant, judging from 

 the condition in which they are grouped on the sandstone, and although 

 the specimens are obscure and too imperfect for positive determination and 

 description, it has been thought best to designate them b}^ name, as they 

 will undoubtedly prove a characteristic form over a certain region and of 

 a limited horizon. The sandstone is marked on the layers in which they 

 are found, by ripple or wave marks, having a width of about three inches, and 

 indicates a near proximity to a shore-line over the area where they were 

 obtained, and that the individuals are probably stranded specimens. A 

 single very imperfect impression of a Lamellibranchiate shell is present 

 on the same fragments of rock, but too imperfect for determination. 



Formation and locality. — In red sandstones of Jurassic age, 70 feet 

 above the red beds, on the east side of Spearfish Creek, near its junction 

 with the Redwater, Black Hills, Dakota. 



CKINOIDEA. 



PENTACRINIDm 



Genus PENTACRINITES Miller. 



PENTACRINITES ASTERISCUS. 



Plate 3, figs. 1, 2. 



Pentacrinus asteriscus M. & H., Proc. Acad. Nat. Sci. Phil. March, 1858, p. 49, iMd., Oct. 



I860, p. 419. 

 Pentacrinites asteriscus M. & H., Pal. Upp. Missouri, p. 67, PI. iii, fig. 2. 

 Pentacrinites asteriscus (M. & H.) White, Pal. Eept. Lieut. Wheeler's Eept. U. S. Geol. 



Surv. 100th Meridian. 

 Pentacrinites asteriscus t (M. & H.) H. & W., Geol. Expl. Fortieth Parallel, vol. iv, p. 



280, PI. 6, fig. 10. 



Messrs. Meek and Hayden describe this species from rocks of Jurassic 

 age at the southwest base of the Black Hills, but none of them appear to 

 have been obtained in the collections of Mr. Jenney's expedition. The fig- 

 ures on Plate 3, are from examples from the Big Horn Mountains, and are 

 given for the purpose of presenting the form, which is so characteristic a 

 fossil of this formation in the western part of the continent. 



