PALEONTOLOGIC CONTRIBUTIONS 



45 



was made. It is seen at once that this is entirely different from 

 Eugasterella (see pi. XVII, fig. 3), but identical in aspect with 

 Lepidasterella, as here described of L . gy alum (see pi. X, fig. 

 5). We find the same median furrow formed by the sharply 

 rectangular bent ridges, proceeding from the narrow marginal 



Fig. 19, 20 Ptilon aster princeps Hall. Proximal and distal 

 portions of the ray of holotype. Figure 19 x 3; figure 20 x 5. 



plates, and the pores or depressions within the spaces delimited by 

 the hooklike ridges. It was stated under the description of 

 Lepidasterella gyalum, that in the similar and closely 

 related Helianthaster the authorities still disagree as to whether 

 the median furrow is the ambulacral furrow or the ambulacrum 

 itself, and correspondingly whether the adjoining plates are the 

 ambulacra or the adambulacra. From the presence of the trans- 

 verse hooklike ridges, the longitudinal bars of which serve for the 

 attachment of the transverse ventral muscles, and the identity of 

 the structure of the actinal side with that of such primitive 

 Asteroidea as Uranaster where identical ridges mark the ambula- 

 cral plates, we infer that also here we have before us a median 

 ambulacral channel, two columns of ambulacrals with ridges and 

 two columns of adambulacrals. 



While in the proximal portion of the ray it would seem impos- 

 sible to discern more than two columns of plates whose separating 

 suture is inside of the knobs upon the crests, the distal younger 

 portion of the rays suggests a further division of the crest by a 

 suture. 



The fragments of the disk show this to have been highly alate, 

 furnished with a marginal row of plates and the interbrachial 

 divisions forming so acute an angle that the starfish had probably 

 a greater number of rays. Combining the fact that the aspect arid 



