REPTI I.I A \ AGE. JURASSIC PERIOD. 67 



Pcutacrinites nateriscus. 



(I'LATK III, Fig. 2, a,b, and annexed cut?) 



Penlaerinui (utrritcui, Mine & HATDK.X, Proceed. Acad. Nat. Sot. I'hila. March, 1858, p. 49 ; Men & HATDBX, Ib. 



Oct. 1860, 419. 

 Comp. Penlacrima tcalarii, OOLDF. Petrefact. Oerm. tab. 62, fig. 3 ; also Quenntedt Der. Jura, tab. 13, flg. 49-S7. 



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

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

 mutter. '1 IK 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 all 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 difference or identity can be established by a . 



, . Pentacnnitet mttructut 



comparison of specimens. North p^ MMr> 



Locality iiit<l /loxltinii. Associated with other Jurassic fossils 

 at the southwest base of Black Hills ; and opposite Red Buttes, North Platte River. 

 (Type 220.) 



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

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

 Hirer Oronp, in Ohio, Kentucky, and Indiana, as w*ell as New York. Rafinesqne'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. 



