REPTILIAN AGE. JURASSIC PERIOD. 



67 



Pentacrinites asteriscus. 



(Plate III, Fig. 2, a, b, and annexed cut ?) 



Pentacrinus asteriscus, Meek & Hatden, Proceed. Acad. Nat. Sci. Phila. March, 1858, p. 49 ; Meek & Hatbbn, ib. 



Oct. 1860, 419. 

 Comp. Pentacrinus scalaris, Goldf. Petrefact. Germ. tab. 62, fig. 3 ; also Quenstedt Der. Jura, tab. 13, figs. 49-57. 



Our knowledge of this crinoid is entirely derived from detached segments of its 

 column, and other parts, as seen imbedded in a sandy matrix, cemented by calcareous 

 matter. The joints of the column may be characterized as rather small, thin, very 

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

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

 the centre of each of these joints, there is a minute circular perforation, 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 applies more particularly to the largest sized specimens, measur- 

 ing about 0.18 inch across from point to point of the opposite angles (see PI. Ill, 

 fig. 2, a, b.) Associated with these, there are smaller joints, 

 varying from 0.05, to 0.10 inch in diameter, having propor- 

 tionally shorter and broader rays, which are usually less angular 

 at the points than those of the larger ones. These may possibly 

 prove to belong to another form, though it is quite as probable 

 they are only joints of smaller individuals of the same species. 

 The annexed cut represents some of these smaller less distinctly 

 angular columns, from a locality on North Platte River. 



The specimens are aU so very similar to the corresponding parts 

 of P. scalaris, Goldfuss, that after more careful comparisons we 

 are inclined to the opinion that they may possibly prove to belong 

 to that species. Still, as they are all much smaller than those 

 figured by Goldfuss and Quenstedt, and none of them have the 

 points of the rays so rounded, we have concluded to retain our 

 name until their dijfference or identity can be established by a 

 comparison of specimens. 



Locality and position. — Associated with other Jurassic fossils 

 at the southwest base of Black HiUs ; and opposite Eed Buttes, North Platte River. 

 (Type 220.) 



Pentacrinites asteriscus ? 

 North Platte River. 



for which Prof. Hall subsequently proposed the name Heterocrinus (Pal. N. Y. Yol. I) ; which has 

 a distinctly pentagonal column, and is common in the Blue Limestone of the age of the Hudson 

 River Group, in Ohio, Kentucky, and Indiana, as well as New York. Rafinesque's name, however, 

 cannot be adopted for this Palaeozoic group, since he gave no characters by which either the genus 

 or the typical species, could be certainly identified. 



