NEW YORK STATE MUSEUM 



from the Rochester shale. Of the latter the Museum, through the 

 liberality of Mr Frank Springer, possesses the genoholotype, and of 

 the former it contains a number of specimens which exhibit fea- 

 tures not shown in the two type specimens. 



24 25 



Fig. 24, 25 Hallaster forbesi (Hall). 24 Diagrammatic view of 

 actinal side of ray (x 5). 25 Abactinal side of ray (x 5), spines on left 

 broken away 



James Hall has quite correctly figured the outline of the actinal 

 aspect of the ray of Hallaster in the 20th Museum Report, 1867, 

 plate 9, figure 6. A later diagram, giving the sutures between the 

 ambulacrals and adambulacrals more correctly is furnished by 

 Schuchert ,in the Revision of the Paleozoic Stellei"oidea, page 255, 

 figure 31, The abactinal side of the ray was correctly described by 

 Stiirtz 1 but has not yet been figured. The oral or mouth angle 

 plates are short and stout and directly attached to the column of the 

 adambulacral plates, while small ambulacral plates seem to con- 

 tinue between them. It is, however, quite possible and even 

 apparent that this condition is due to a contraction of the mouth 

 parts. 



The disk is distinctly pentagonal in the two best preserved speci- 

 mens and the rays are so arranged that the angles of the pentagon 

 lie between the rays. The abactinal side of the disk exhibits 

 tumid, coarse, irregular plates and many blunt, articulated spines 

 like those on the rays. On the latter they are arranged in series of 

 three to five along the distal edges of the adambulacrals. They 

 are mostly blunt, rod-shaped or even slightly club-shaped as 

 figured by Hall, with a distinct broad articulating base. 



As the published drawings give only an inadequate idea of the 

 strange ophiuroid aspect of this ancient auluroid, we have repro- 

 duced a restoration of the abactinal side in plate 19. 



iStitrtz, N. Jahrb. fur Min. etc., 2,: 150'. 1886. 



