OPHIACANTHA, 1 Lf 
7. OPHIACANTHA. 
Ophiacantha, M. Tr. Syst. Ast. (1842) p. 106; Liitk. Danske Selsk. 
Skrift. v. (1859) p. 65; Lyman, Ill. Cat. M. C. Z. i. (1865) p. 98 ; 
td. Chall. Rep, Oph. (1882) p. 178. 
No tooth-papille; teeth; mouth-papille 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, Retziws, Diss. Ast. (1805) p. 35. 
Ophiura retzii, Né/sson, Coll. Zool. Scan. (1817) p. 15. 
Ophiacantha spinulosa, M. Ti, Syst. Ast. (1842) p. 107; Sars, Norg. 
Echin. (1861) p. 15; Lyman, Il. Cat. Mus. C. Z. 1. (1865) p. 93 ; 
Jarzynsky, Trans. Petersb. Soc. Nat. i. (1870) p. 818; Marenzell. 
Denkschr, Ak. Wien, xxxv. (1878) p. 382; Dunc. § Slad. Mem. 
Echin. Greenl. (1881) p. 68. 
Ophiocoma arctica, M. Tr. Syst. Ast. (1842) p. 108. 
Ophiacantha greenlandica, M. Tr. Arch. f. Nat. 1844, p. 183. 
Ophiocoma echinulata, Forbes, Sutherland’s Voy. (1852) ii. p. cexv. 
Ophiacantha bidentata, Ljn. Gtfv. K. Vet.-Akad. Forh. 1871, p. 652 ; 
Lyman, Chall. Rep. Oph. (1832) p. 186; td. Bull. Mus. C. Z. x. 
(1883) p. 260; Hoyle, Proc. R. Soc. Ed. xii. (1884) pp. 709, 710, 
712; wd. Proc. R. Phys. Soc. Ed. viii, (1884) p. 142. 
A moderately-sized species, with projecting 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 and below. Arm-spines 
six or seven, the uppermost the longest, and as much as 5°5 mm. 
long. The mouth-papille 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). 
