OPHIACANTHA. 121 



7. OPHIACANTHA. 



Ophiacantha, M. Tr. Syst. Ast. (1842) p. 106 ; Liltk. Danske Selsk. 

 Skrift. v. (1859) p. 65; Lyman, III. Cat. M. C.Z. i. (1865) p. 93 ; 

 id, Chall. Rep. Oph. (1882) p. 178. 



Xo tooth-papillae ; teeth ; mouth-papilla3 numerous. Radial 

 shields elongated, often obscured. Disk spiny or thorny. Arm- 

 spines hollow, often rough and elongated. Long bursal slits. 



Key to the Species. 



Arm-spines slightly thorny 1. O. bidentata. 



Arm-spines not thorny 2. O. spectabilis. 



Arm-spines translucent 3. O. abyssicola. 



1. Ophiacantha bidentata. 



Asterias bidentata, Retzius, Diss. Ast. (1805) p. 33. 



Ophiura retzii, Nilsson, Coll. Zool. Scan. (1817) p. 15. 



Ophiacantha spinulosa, M. Tr. Syst. Ast. (1842) p. 107 ; Sars, Norg. 



Echin. (1861) p. 13; Lyman, III. Cat. Mus. C. Z. i. (1865) p. 93 : 



Jarzynsky, Trans. Petersb. Soc. Nat. i. ( 1870) p. 318 ; MarenzeU. 



Denkschr. Ah. Wien, xxxv. (1878) p. 382; Dune. 8f Slad, Mem. 



Echin. Greenl. (1881) p. 68. 

 Ophiocoma arctica, M. Tr. Syst. Ast. (1842) p. 103. 

 Ophiacantha groeulandica, M. Tr. Arch.f. Nat. 1844, p. 183. 

 Ophiocoma echinulata, Forbes, Sutherland's Voy. (1852) ii. p. 



cexv. 



Ophiacantha bidentata, Ljn. CEfv.K. Vet.-Akad. Fork, 1871, p. 652 

 Lyman, Chall. Rep. Oph. (1882) p. 186; id. Bull. Mus. C. Z. x. 

 (1883) p. 260; Hoi/lc, Proc. R. Soc. Ed. xii. (1884) pp. 709, 710, 

 712 ; id. Proc. R. Phys. Soc. Ed. viii. (1884) p. 142. 



A moderately-sized species, with projectiug lateral arm-plates. 

 Disk covered with very short spines. Arm-spines finely serrated, 

 rather long, not transparent. Arms five or six, most remarkable 

 for the prominent ridges formed by the lateral arm-plates on each 

 side ; these plates meet in a suture above aud below. Arm-spines 

 six or seven, the uppermost the longest, and as much as 5-5 mm. 

 long. The mouth-papillae not numerous, but inconstant in number, 

 and to some extent in position, as is the mouth-shield in form. 

 Except at base of arm a single tentacle-scale. Diameter of disk 

 13 mm. ; arms very fragile. 



Colour, in spirit, whitish. 



A very variable species and one exhibiting great changes during 

 growth. 



Distribution. Both sides of North Atlantic, as far south as Cape 

 Cod on the west, but not south of Faeroe on the east ; Arctic Ocean 

 20-2335 fms. 



a, b. Faeroe Channel, 440 fms. ' Porcupine ' Exp. (St. 51 ) . 



c. Faeroe Channel, 384 fms. ' Porcupine ' Exp. (St. 52) . 



