fi-ARK] ASTER IAS DUIJITM. 31 



tlie previous vSpocies, from which, on the other huiul, it is .separated by 

 the different shape of the divsk and of the under and upper arm phites. 



Localit;/ and gcolof/ical horizon. — The shib containing the specimens 

 described is from the Denison beds of the Washita division of tlie Co- 

 manche series (Lower Cretaceous), 6 miles north of Fort Worth, on the 

 banks of Fossil creek. Ft is found associated with Ostrca <ina(Jriplivata 

 Shumard, Stearusia KobhinftiAWiitt', and Lciociduris hemiyranosus {^hxi- 

 mard). 



CoUirtion. — U, S. National Museum. 



STET^T^ERIB^. 



Body star-shaped or pentagonal, composed of a central disk and five 

 prolongations of the same, called arms, that are ])ortious of the body 

 proper. Integument strengthened by calcareous plates irregularly ar- 

 ranged. Ambulacral furrow uncovered. 



ASTEEIAS Linnreus. 

 AsTERiAS? DUBiUM Whitfleld." 

 Plate V, Fig. 2. 



Aaterxas^. duMiim Whitfield, 1877. Prelim. Kept. Pal. Black Hills, p. 15. 

 Jsterias^ dnhiitm Whitfield, 1880. Geol. Black Hills of Dakota, pp. 344, 345, PI. 3, 

 Fig. 3. 



Di'termmative characters. — Imperfectly preserved forms of small size, 

 with slender flexuous arms, apparently covered superiorly with longi- 

 tudinal rows of i)lates. 



Diniensiotis. — Length of arms, f inch to IJ inches. 



Beficription. — This interesting but doubtful form is thus characterized 

 by Whitfield: "The specimens are not in condition to afford a full de- 

 scription of their specific characters. They are of small size, the rays 

 being from three-fourths of an inch to one and one-fourth inches long, 

 measuring from the center of the body. The rays are slender and flex- 

 uous, most of them being more or less curved in their direetion and 

 elevated along the middle, as shown on a gutta-percha cast taken in a 

 natural mold of a group of three individuals. The upper surface is 

 subangular, and in structure they are apparently composed of small 

 unitbrm plates, placed in longitudinal rows. The center of the body 

 or disk is marked by an obscurely pentangular depression on tlie upper 

 surface. None of the specimens show the under side of the body or 

 rays, so that the characters of these parts are entirely unknown. 



"The species appears to have been somewhat abundant, judging from 

 the condition in which they are grou])ed on tlie sandstone, and, although 

 the specimens are obscure and too imi)erfect for positive determination 

 and description, it has been thought best to designate them by names, 

 as they will undoubtedly prove a characteristic form over a certain re- 



