TROPHODISCUS, A NEW SEA STAR FROM KAMCHATKA. 



By Walter K. Fisher, 



Of Stanford University, California. 



The new genus and species described herewith belongs to the family 

 Astropectinidae, and stands near to Leptychaster, especially to Lepty- 

 chaster propinquus and L. anomalus. In Leptychaster, or rather in 

 those species of the genus found in the northern hemisphere, the 

 gonads have a very characteristic distribution which so far as now 

 known is not found elsewhere among starfishes. In the great major- 

 ity of sea stars the gonads are confined to the interradial region and 

 usually form a single tuft or cluster of tubules on either side of the 

 interbrachial septum. In Leptychaster this is true of the ovaries only, 

 while the testes form a series of clusters hanging from the genital 

 stolon, and extending about a third the length of the ray measured 

 along the side. In the new genus, as weU as in Dipsacaster, Tethy- 

 aster, and several other genera of the Astropectinidae both the ovaries 

 and testes are so distributed, without any apparent difference, other 

 than the cellular structure. The gonads are, therefore, serially 

 arranged. 



Trophodiscus may be distinguished from the shorter-rayed species 

 of Dipsacaster by the uncovered, relatively smaller madreporic body, 

 by the interruption of the papular area along the midradial line 

 (where, in Dipsacaster the papulae are normally largest), and by the 

 wholly unarmed inferomarginals (except D. anoplus Fisher). No 

 species of Dipsacaster, so far as known, broods its young. 



TROPHODISCUS, new genus. 



Characters. — Near to Leptychaster Smith, but differingin having both 

 ovaries and testes serially arranged along each side of the proximal 

 half of the ray. Form stellato-pentagonal ; with conspicuous mar- 

 ginals, large compact paxiUae, carinated actinal intermediate plates, 

 and a pectinate furrow armature; no enlarged marginal spines; an 

 incomplete interradial series of actinal intermediate plates; madre- 

 poric body uncovered; papulae absent from center of disk and a very 

 narrow radial area. Young carried on back of the female, among the 

 paxiUae. 



Type. — Trophodiscus almus, new species. 



PROCEEDINGS U. S. NATIONAL MUSEUM. VqL. 52-No. 2180. 



367 



