EEVISION OF PALEOZOIC STELLEROIDEA. 53 



rise to the PalasterinidaB. This line of change is not at all so pro- 

 ductive of genera as the former. Finally, a third phyletic line is 

 established through larval adaptation, causing a sixth ray to develop 

 and thereafter pairs of rays, resulting in the multi-rayed asterids of 

 the family Lepidasterida}, 



These phyletic lines may be expressed taxonomically as follows: 



Superfamily Promopaliseastcracea, new. 



Includes families Hudsonasteridse, Palseasteridsc, Proniopalseasteridae, and 

 Xenasteridse. The Neopaloeasteridae developed out of the Promopalaeasteridse. 

 Superfamily Palasterinacea, new. 



Includes family Palasterinidse. 

 Superfamily Lepidasteracea, new. 



Includes family Lepidasteridse. 



HUDSONASTERID^, new family. 



Most primitive known Phanerozonia. 



Small, five-rayed, heavily plated asterids, with narrow ambulacra! 

 furrows and slightly alternate ambulacralia. The incipient inter- 

 brachial arcs are occupied by single axillary marginal plates. Abac- 

 tinallythe rays have five columns of ossicles, the radials in the center 

 being bomided on either side by the supramarginals and inf ramai^inals ; 

 the latter margin the rays and the ossicles of adjoining columns alter- 

 nate with one another. There are no accessory ray plates of any 

 kind. The disk has a prominent central disk piece separated by a 

 small number of accessory disk plates from a ring of five large basal 

 radials and five large basal interradial ossicles. Spines rudimentary 

 and apparently restricted to the adambulacrals and inframarginals. 



This family contains the genera Hudsonaster Stiirtz and Siluraster 

 Jaekel. 



Genus HUDSONASTER StUrtz. 



Plates 1-6. 

 Palxastcr (part) of authors. 

 Hudsonaster Sturtz, Verh. naturh. Ver. preuss. Rheinl., etc., vol. 56, 1900, 



pp. 224, 225. 

 Protopalseaster Hudson, Ottawa Naturalist, vol. 2G, 1912, p. 25; vol. 27, 1913, 



pp. 77-84. — Raymond, Ottawa Naturalist, vol. 26, 1912, p. 105 (genoholo- 



type, P. narrawayi). — Spencer, Mon. Brit. Pal. Aaterozoa, pt. 1 (Palseontgr. 



See. for 1913), 1914, p. 21. 



The name is derived from the "Hudson River formation," an 

 Ordovicic series of strata of long endurance. If the stratigraphic 

 term is used correctly, then these rocks have as yet furnished no 

 starfishes of this genus; for this reason Hudsonaster is a misnomer 

 and has no significance, but under the rules of nomenclature it must 

 be accepted. 



Generic characters. — Disk small and without actual interbrachial 

 arcs. Rays five, short, tapering rapidly. 



