JTJKASSIC ECHINODEBMATA. 27 



Pentacrinites asteriscus Whitfield, 1880, Paleontology of Black Hills of Dakota: U. S. Geog. and Geol. Survey Rocky 



Mtn. Region, p. 345, PI. Ill, figs. 1, 2. 

 Pentacrinus asteriscus Peale, 1880, U. S. Geol. and Geog. Survey Terr. Bull., vol. 5, No. 1, p. 120. 

 Pentacrinus asteriscus Clark, 1S93, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Pentacrinus asteriscus Clark, 1893, TJ. S. Geol. Survey Bull. 97, pp. 26, 27, PI. II, figs. 2a-d. 

 Pentacrinus asteriscus Weed and Pirsson, 1898, U. S. Geol. Survey Eighteenth Ann. Rept., pt. 3, p. 478. 

 Pentacrinus asteriscus Stanton, 1S99, U. S. Geol. Survey Mon., vol. 32, pt. 2, p. 608. 

 Pentacrinus asteriscus Knight, 1900, Wyoming Exper. Sta. Bull. 45, PI. IV, fig. 2. 

 Pentacrinus asteriscus Darton, 1901, U. S. Geol. Survey Twenty-first Ann. Rept., pt. 4, p. 521. 



Determinative characters. — Columns composed of medium-sized pentagonal joints with 

 moderately deep reentering angles; crenulated ridge of suture strongly petaloidal; column per- 

 forated by canal of medium size. 



Dimensions. — Column: Diameter of joint 2 to 5 millimeters. 



Description. — First described by Meek and Hayden from several column joints found in the 

 Black Hills. When they redescribed and figured the species in 1865 they combined with the 

 earlier forms certain smaller column joints found at Red Buttes on North Platte River, figures 

 of which were given in the text, but these have been recently doubtfully referred by Springer to 

 Isocrinus Icnighti. Meek and Hayden in this later publication state that their "description 

 applies more particularly to the largest-sized specimens" from the Black Hills and that the two 

 figures on their Plate III represent these forms, which must therefore be regarded as the type 

 of the species. 



Many similar isolated column joints have been found widely scattered throughout the 

 Rocky Mountain region by different geologists and most of them are regarded by the author as 

 belonging to this species. Since it has been clearly demonstrated that the column joints vary 

 in the different portions of the stem of nearly all crinoids it is evident that several different 

 species and possibly even different genera may be represented among these forms. 



The specimens referred to this species are of moderate size, clearly pentagonal, and with 

 moderately deep reentering angles, the points of the rays being sharp, and the suture joints 

 apparently uniting to form a compact column. 



Hall and Whitfield referred doubtfully to Pentacrinites asteriscus Meek and Hayden certain 

 specimens collected by Hayden in Nevada from "limestones of supposed Triassic age." There 

 is much doubt as to this form, but it evidently does not belong to P. asteriscus. 



Related forms. — The species presents some points of difference from P. whitei, which has 

 been generally regarded as belonging to it. Its column joints are generally somewhat smaller, 

 are not alternating, do not have as deep reentering angles, and its rays are somewhat sharper. 

 The crenulation of its petaloid area is also somewhat different. This species is somewhat similar 

 to Pentacrinus shastensis of the Pacific coast, but the latter is of slightly different form and gen- 

 erally has shallower reentering angles. 



Localities. — South and southwest base of Black Hills, South Dakota (type), and Red Buttes, 

 Wyo. ; South Dakota, Idaho, and Colorado (Meek) ; southeastern Idaho and western Wyoming 

 (Peale); Black Hills, South Dakota (Whitfield) ; Sundance formation (Upper Jurassic), Black 

 Hills, South Dakota (Darton). 



Geologic horizon. — Jurassic. 



Collection. — U. S. National Museum (220); University of Kansas. 



Pentacrinus whitei Clark. 



Plate III, figures 3a-c. 



Pentacrinus asteriscus White, 1875, U. S. Geog. Surveys W. 100th Mer. Rept., vol. 4, pt. 1, p. 162, PL XIII, figs. 6a-b. 

 Pentacrinus whitei Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Pentacrinus whitei Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 27, 28, PL III, figs. 2a-d. 

 Pentacrinus whitei Springer, 1909, U. S. Nat. Mus. Proa, vol. 36, p. 188. 



Determinative characters. — Column composed of large, thin, alternating, pentagonal joints 

 with deep reentering angles; crenulated ridges of suture with strong pentaloid arrangement; 

 column perforated by canal of medium size. 



