REVISION OF PALEOZOIC STELLEROIDEA. 



255 



bulacral ossicles. In Hallaster the lateral wings of the plates curve 

 round the podial openings proximally, while in Lapworthura they do 

 so distally. Further, the side plates of the latter genus bear spines 

 along their sides, while in the former genus they are restricted to the 

 distal ends of the plates. 



HALLASTER FORBESI (Hall). 



Text fig. 31. 



Protaster forbesi HALL, Nat. Hist. N. Y., Pal., vol. 3, 1861, p. 134, pi. 7 A, figs. 

 8-10; Twentieth Rep. N. Y. State Cab. Nat. Hist., 1868, p. 293, pi. 9, figs. 5, 

 6; rev. ed., 1868=1870, p. 336, pi. 9, figs. 5, 6. QUENSTEDT, Petrefacten- 

 kunde Deutschlands, vol. 4, 1876, p. 134, pi. 95, fig. 13. STUKTZ, Palaeonto- 

 graphica, vol. 32, 1886, pp. 78, 83. 



Hallaster forbesi STURTZ, N. Jahrb. fur Min., etc., 1886, vol. 2, p. 150. 



The original description will not be repeated here because it is 

 faulty and was later corrected by Hall. 



Hall's description of 1868. P. forbesi "has a circu- 

 lar disk, composed of squamif orm spiniferous plates 

 and five long flexuous rays. These rays I have 

 [originally] represented as composed, on the lower 

 side, of a double range of [adambulacral] plates, as 

 described and represented by Professor Forbes, but 

 finding outside of these a range of small ossicles 

 [side plates] to which are attached the spine bases, 

 these have been shown as a part of an articulating 

 spine (in the illustration, plate 7 A 1 ), an unnatural representation, 

 which I am now able to correct. 



"In the species from the Lower Helderberg group, Protaster forbesi , 

 the ventral surfaces of the rays are composed of an ambulacral and 

 adambulacral series of plates on each side [there are no ventral ray 

 plates]. The ambulacral plates are obliquely quadrangular and alter- 

 nating in a slight degree [in the type they are opposite] ; the adambu- 

 lacral plates as seen from the lower side are narrow, elongate, oblique, 

 and laterally imbricating, presenting the appearance of an oblique 

 ridge with the anterior extremity projecting, and forming the point 

 of attachment for the spines, with which each one is furnished. [These 

 spines are striated longitudinally.] When the ray is abruptly curved, 

 these plates project outward, sometimes almost rectangularly; and 

 when at the same time the ambulacral area is obscured by aclhering 

 matrix, these plates might readily be mistaken for appendages of 

 the inner ranges. The pores are comparatively large, truncating 

 the outer adjacent angles of the ambulacral plates, while the base 

 of one adambulacral plate and the side of another form the exterior 

 margin. The centers of the upper sides of the rays are composed of 



FIG. 31. ACTINAI, BAT 

 PLATES OP HALLASTER 

 FORBESI (HALL). OP- 

 POSITE AMBULACRALS, 

 AND THE SIDE PLATES. 



* Nat. Hist. New York, Pal., vol. 3, 1861. 

 50601 Bull. 8816 17 



