REVISION OF PALEOZOIC STELLEROIDEA. 247 



Genoholotype and only species. — 0. lymani Stiirtz (citations as 

 above.). Lower Dovonic, Bundenbacli, Germany. 



Genus TREMATASTER Worthen and Miller. 



Tremataster Worthen and Miller, Geol. Surv. Illinois, vol. 7, 1883, p. 330. — 

 Miller, N. Amer. Geol. Pal., 1889, p. 28G. — Gregory, Proc. Zool. Soc. 

 London for 1896, 1897, p. 1037. 



Original description. — "Body stellate, central part discoid, rays 

 long, flexiious, and gradually tapering. Rays consisting of a double 

 series of ambulacral plates, forming, together, a subcuneiform se- 

 ries, Avith the tapering ends directed toward the apices of the rays 

 and uniting with the larger ends of the succeeding double plates, 

 upon each side of which there is a series of curved adambulacral 

 plates, wliich form the margms of the rays. The pores are large 

 and situated between the contracting sides of the ambulacral plates 

 and the concave sides of the curvmg adambulacrals. Four plates 

 border upon each pore though nearly surrounded by two of them. 

 Plates 10. Dorsal surface unknown. 



"This genus is distinguished by the parallel arrangement of the 

 ambulacrals and adambulacrals, instead of the alternate order, and 

 by the large pores," 



Gregory's diagnosis is as follows: "Disk with concave inter- 

 brachial outlines. No margmal plates. Ambulacral ossicles short. 

 Adambulacrals present." 



GenoJiolotype. — T. difficilis Worthen and Miller. T. {?) decheni 

 (Dewalque) may also belong here. 



TREMATASTER DIFFICILIS Worthen and Miller. 



Tremataster difficilis Worthen and Miller, Geol. Surv. Illinois, vol. 7, 1883, 

 p. 330, pi. 31, figs. 3tf, 36. 



Original description. — "Body stellate, disk small, rays long, 

 flexuous, and gradually tapering. Ambulacral plates subtrigonal, 

 elongated, and united upon their straight faces in parallel order, 

 so as to form a series of subcuneiform sections at the bottom of 

 the ambulacral groove, with the tapering end of each directed toward 

 the apex of the ray, and uniting with the larger end of the next 

 succeeding double plate. 



"Adambulacral plates parallel with the ambulacrals, and each 

 forms a curve from the larger end of an ambulacral toward the 

 apex of the ray, to unite with the next succeeding adambulacral as 

 it curves away from its attachment to the ambulacral. By this 

 order of construction the adambulacrals are fixed, at one end, to 

 the ambulacrals, while the other end moves upon the curved surface 

 of an adambulacral so as to allow the same lateral flexibility of 

 the rays, secured in other genera by the alternate arrangement of 



