FOURTH REPORT OF TttE DIRECTOR I907 63 



made to solve the difficult problem of removal of the matrix and 

 exposure of structural details. Roemer figured the best but not the 

 largest of his specimens [pi. 28] and the number of arms assigned 

 by him to this species is 16. Stiirtz finds this number also (14-16). 

 At all events the species is large and its arms relatively numerous 

 in contrast with other Paleozoic ophiurans. The disk is mostly 

 covered by the converging arms and the length of any one of the 

 latter from the point where it becomes free to its tip is almost equal 

 to the axis of the disk which in both the German and American 

 specimens seems not to be normally circular but often elliptical. 



The New York specimens, H e 1 i a n t h a s t e r g y a 1 u m 

 nov. are smaller than H . r h e n a n u s . The arms are more 

 numerous and appear to be quite uniformly 24-25. Compared to 

 H . r h e n a n 11 s they are relatively short, but very long compared 

 with the size of the disk which is much suppressed, and on none 

 of the specimens, all showing the oral surface, is any distinct evi- 

 dence of it visible, so deeply do the arms cut into it and so closely 

 do they lie together. Notwithstanding this apparent retreat of the 

 disk the madreporiform plate is very large. This organ is preserved 

 in but one example and but here it overlaps two adjoining inter- 

 brachial angles and the mouth parts pertaining thereto. Instead of 

 being a flat or concave elongate- plate as in H . r h e n a n u s it is 

 highly convex and circular; its surface markings less distinct and 

 coarse than in that species. 



The great oral aperture is margined by a series of pronounced 

 " jaws " or sharp projecting elevated angles the sides of which take 

 origin from the margins of adjoining arms. These oral projections 

 are slightly expanded at their tips into blunt points comparable t^ 

 but smaller than the " Hocker " of H . r h e n a n u s but like thc*^ 

 carry small spines projecting inward. The solidity and strength oi 

 these mouth parts is indicated by their prominence and elevation as 

 shown in figure. It is probable that in this expression there is repre- 

 sented a combination of dorsal and ventral structure with the latter 

 predominant by compression. Stiirtz has been able to distinguish 

 the dorsal and ventral details in II . r h e n a n u s and assigns to 

 the former a pair of divergent thickened crescentic narrow and 

 vertical plates departing from the axis of each arm and each member 

 joining one of the adjacent pair, thus producing the projecting oral 

 processes. In our specimens it is not possible to discriminate these 

 structures further than to recognize in them a combination of these 

 oral plates with the spinous oral processes. The reentrant angle at 

 the base of each arm is narrow, long and acute, much more extreme 



