A REMARKABLE NEW SEA STAR FROM JAPAN. 



By W. K. Fisher, 

 Of the Hopkins Marine Station of Stanford University. 



Lysasfrosoma is remarkable for being the only genus known which 

 is very closely related to Pycnopodia Stimpson. The latter is one of 

 the most distinct types of Asteriidae found in the north Pacific, and 

 ranges from Unalaska to California (south of Monterey Bay). It 

 is significant to discover its nearest relative on the Asiatic side of the 

 north Pacific. 



Genus LYSASTROSOMA Fisher.i 



Diagnosis. — Rays 5, soft and weak; abactinal skeleton reduced to 

 isolated small spinif erous plates sometimes interspersed with vestigial 

 perforated spineless platelets ; marginal skeleton weak ; superomorgi- 

 nals well separated, connected by a chain or festoon of small secondary 

 ossicles; alternate superomarginals reduced in size and spineless; 

 inferomarginals diplacanthid, spaced, sometimes connected by 1 or 2 

 secondary small ossicles; abactinal and marginal spines surrounded 

 by a conspicuous, tough, retractile sheath expanded distally (and 

 bearing numerous small crossed pedicellariae) , that of the infero- 

 marginals common to the 2 spines ; adambulacral plates monacanthid, 

 the spinelets without pedicellariae ; mouth plates broad, with 1 pair 

 of enlarged postoral adambulacral plates in contact ; crossed pedicel- 

 lariae with a conspicuously enlarged tooth on one side of the end of 

 jaw, two or three smaller teeth on the opposite side, and very numer- 

 ous small teeth on the shank. 



Most nearly related to Pycnopodia Stimpson but differing in hav- 

 ing the marginal plates disconnected or joined only by secondary 

 intermediate marginal ossicles; broad mouth plates and enlarged 

 postoral adambulacral plates; more conspicuous marginal circum- 

 spinal sheaths, the inferomarginal being common to two spines; 

 adambulacral plates not sunken below level of inferomarginals ; rays 

 5, not upward of 24. 



Type. — Lysastrosoma anthosticta. 



»Ann. and Mag. Nat. Hist., sec. 9, vol. 10, Dec. 1922, p. 590 (brief diagnosis). 



No. 2493.— Proceedings U. S. National Museum. Vol. 64. Art. 3. 



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