REVISION OF PALEOZOIC STELLEROIDEA. 55 



with the pairs of ambulacral armature pieces. In H. narrawayi above 

 or dorsal to the pair of large oral pieces there is another but smaller 

 and modified pair of ambulacral ossicles clearly also a part of the oral 

 armature. 



Ambulacral grooves originally narrow and regularly tapering. Am- 

 bulacral plates rectangular, practically opposite or very slightly 

 alternating, one to each adambulacral plate. The ambulacralia 

 of each column may be so closely adjoining as to leave almost no 

 space for the podial openings, or there may be laterally between 

 adjoining ossicles very large openings. 



Genolwlotype. — The genotype selected by Sttirtz is Palasterina 

 rugosa Billings. The above generic definition is, however, largely 

 based upon Palseaster incomptus Meek and P. matutinus Hall. 



Distribution. — Restricted to the middle and upper portion of the 

 Ordovicic. The following are the known species: 



H. matutinus (Hall). Trenton. 



H. narrawayi (Hudson). Black River. 



H. milleri, new species. Trenton. 



E. incomptus (Meek). Maysvillian and Richmondian series. 



H. rugosus (Billings). Lower Richmondian, Charleton forma- 

 tion. 



//. hathen, new species. Upper Ordovicic, Girvan, Scotland. 

 Remarks. — Stiirtz is unfortunate in selecting as the genotype of 

 Hudsonaster, Palasterina rugosa Billings, a very poorly laiown starfish 

 from the Richmondian of Anticosti Island. Therefore his original 

 definition of Hudsonaster is not only very imperfect, but the specimen 

 is wrongly interpreted. His characterization of the genus is as 

 follows : 



Of Palasterina rugosa only the abactinal side is known. On the disk occur orna- 

 mented, deeply crenulate, star-shaped plates. Four [the specimen is distorted and 

 has forced into view one of the inlramarginal columns, while the one on the other side 

 of the ray is shoved out of sight] regular and decided columns mark the rays, and of 

 these the outer rows are stronger than the inner columns. The outer columns consist 

 of unmistakable marginal plates [one is inframarginal, the other is a supramarginal 

 column]. According to BilUngs there are even traces of the actinal marginals to be 

 Been from the abactinal side. Spines absent [the usual spines of this genus are also 

 present here]. The arms terminate sharply in points. 



Stiirtz is correct in saying that this species can not be included in 

 Palasterina and also that the genus has come to embrace a variety 

 of unrelated genera. However, he does not say what are the 

 actual generic characters of Hudsonaster, but as P. rugosa is not a 

 Palasterina he concludes that as "new generic names are required 

 I propose Hudsonaster for Palasterina rugosa Billings." This 

 species is undoubtedly congeneric with Palseaster incomptus, a form 

 fully described in this work both from the actinal and abactinal sides, 

 and is therefore taken as the genotype for the above generic defini- 

 tion. 



