LEPTOPTYCHASTER. 65 



Distribution. Both sides of the northern part of the Atlantic, and 

 Arctic Ocean. 7-632 fms. 



a. Faeroe Channel, 60° 0' 0" N., 5° 13' 0" W., 312 fms. < Porcupine ' Exp. 



ASTRO PECTINID.E {see p. 20). 

 ASTROPECTIXIN^ {see p. 20). 



Key to the Genera of Astropectininae. 



A. Superomarginal plates with a prominent 

 ridg-e. 



Superomarginals much smaller than infero- [p. 65. 



marginals 1. Leptoptychaster, 



Superomarginals nearly or quite equal to 



inferomarginals 2. Astropecten,p.66. 



B. No prominent ridge to superomarginals. 

 . Spinelets simple ; ambulacral armature a 



straight series of numerous and uniform 



spinelets 3. Psilaster, p. 68. 



Spinelets in sheath ; ambulacral armature 



an angulated series of a few spinelets, [p. 69. 



not all alike 4. Bathybiaster, 



1. LEPTOPTYCHASTER. 



Leptyehaster, Smith, Ann. § Mag. xvii. (1876) p. 110. 

 Leptoptychaster, id. Phil. Trans, clxviii. (1879) p. 277 ; Slad. Chall. 

 Rep. Ast. (1889) p. 175. 



Flattened, with narrow ambulacra; superomarginals smaller than 

 inferomarginals, intermediate plates extending only partly along 

 the rays. 



1. Leptoptychaster arcticus. 



Astropecten arcticus, M. Sars, Nyt Mag. vi. (1851) p. 161 ; id. Faun. 



lift. Norv. ii. (1856) p. 61, pi. ix. figs. 16-18'; id. Korg. Ech. 



(1861) p. 32 ; Duj. § Hup.Echin. (1862) p. 428. 

 Archaster liitkeni, Barrett, Ann. 8f Mag. xx. (1857) p. 46, pi. iv. 



fig. 3 ; Duj. $ Hup. Echin. (1862) p. 428. 

 Archaster arcticus, Verr. Am. J. Sci. xvi. (1878) p. 373; Storm, Vid. 



Norsk. Selsk. Skrif. Thrond.jhem, viii. (1879) p. 252. 

 Leptoptychaster arcticus, Sladen, Chall. Rep. Ast. (1889) p. 189. 



R = 2-25 r. 



A small species, with a large disk and rapidly tapering arms, the 

 angles between which are distinctly rounded ; the rather narrow 

 ambulacra are bounded by a row of long spines arranged by threes 

 on each adambulacral, outside of which are other rows so closely 

 packed as to be almost disorderly in their disposition ; the inter- 

 mediate plates which fill up the rather large interbrachial area, but 



p 



