162 JUKASSIC PEKIOD. 



CHAPTER VIII 



MESOZOIC AGE. 



JUEASSIO PERIOD. 



RADIATA. 



Class ECHINODERMATA. 



Oedee CRINOIDEA. 



Family PENTACRINID^. 



Genus PENTACEINUS Miller, 1821. 

 Pentacrinus asteriscus Meek and Hayden. 

 Plate XIII, flg. G a and 6. 

 Pentacrinus asteriscus Meek and Haydeu 1864, Paleout. Upper Missouri, C7. 



This species was described by Meek and HaySeu from fragments of 

 the column and branches alone, which were collected from Jurassic strata 

 at the southwest base of the Black Hills, North Platte River. They char- 

 acterize the joints of the column thus: — " Rather small, thin, very symmetri- 

 cal, pentagonal, star-shaped bodies, the rays of which are usually a little 

 longer than wide, and somewhat acutely angular at their extremities. 

 Through the center of each of these joints, there is a minute cu'cular per- 

 foration, from which five lance-oval petaloid areas radiate, one to the 

 extremity of each of the angles ; the areas being bounded on each side by 

 rather narrow, slightly-elevated, crenulate margins. This description 

 apphes more particularly to the largest-sized specimens, measiu'ing about 

 0.18 inch from point to point of the opposite angles. Associated with these, 



