138 NEW YORK STATE MUSEUM 



" secondary jaws " and " suboral epineurals." On the supposition, 

 however, that P. narrawayi presented an apical aspect, these 

 plates presented much difficulty, for, so far as known, this type 

 specimen is the only fossil sea star showing two pairs of floor plates 

 one over another and with their common faces meeting in the same 

 interradial vertical plane as those of the first pair of cover plates 

 or between what is commonly called the " adambulacral jaw " and 

 the apical skeleton. The apparent direction of their movements 

 would seem to aid in thrusting food out of the oral cavity, not into 

 it. They may have become double chains of ossicles connecting the 

 apical surface of the axillary interradial with the first cover plates 

 and, by means of muscular attachments, serving to draw the latter 

 apically, but whatever function we assign them (and their form 

 hardly allows us to regard them as vestigial and functionless) we 

 must admit that they no longer represent a primitive condition. 



Although Schuchert (1915, page 34, figure i) gives a ventral 

 view of a "Theoretic Phylembryo of Stelleroidea. . . . Based 

 on Hudsonaster," he pays no attention to the peculiar features noted 

 above but draws his first floor plates as he finds them in U r a - 

 sterella girvanensis. If Hudsonaster is at all like Pro- 

 topalaeaster, only four floor plates could be seen beside the first six 

 cover pieces drawn. The latter also in both Hudsonaster and 

 Urasterella are never set exactly opposite the floor plates but slightly 

 nearer the oral aperture. 



References 



Bather, F. A. 1900 The Crinoidea in Lancaster's, "A Treatise 



on Zoology "' Adam and Charles Black. 

 London. 



191 5 Studies in Edrioasteroidea I-IX. The 



author. "^Fabo,"Marryat Road, Wimble- 

 don, Eng. 



Fisher, W. K. 191 1 Asteroidea of the North Pacific and Ad- 

 jacent Waters, Part i. U. S. Nat. Mus. 

 ^ Bui. 76. 



Gregory, J. S. 1900 The Stelleroidea in Lancaster's "A Treatise 



on Zoology." 



Hudson, G. H. 1911 Studies of Some Early Siluric Pelmatozoa. 



N. Y. State Mus. Bui. 149. 



— '■ 1912 A Fossil Starfish with Ambulacral Cover- 



ing Plates. Ottawa Naturalist, p. 21- 

 26, 45-52 (May, June- July) 



