534 W. DE MORGAN. 



Station VII. ttt fathoms. 5 specimens. 



Bell describes it as a rather small species. The two largest Huxley 

 dried specimens have a disc diameter about 5 mm. 



It is at once distinguishable from Ophiactis Balli by the unequal 

 thickened disc scales and spines, and the large radial plates. 



Ophiacantha abyssicola, G. 0. Sars. 



Station XII. 246 fathoms. 17 specimens. 

 Station XIII. 412 fathoms. 3 specimens. 



All are young animals. The largest has a disc 5*5 mm. diameter, 

 and arm 20 mm. long, as nearly as could be measured on a dry speci- 

 men. Bell (1) describes abyssicola as " a small species." 



Diameter of disc 9 mm., and K said to = 10 r. 0. abyssicola has 

 been obtained by the Travailleur et Talisman Expedition (6), p. 288, 

 between Lat. N. 35° 42', Long. W. 8° 40', and Lat. K 44° 5', Long. W. 

 9° 25' 40" in depths from 112 to 1226 metres, and by the Caiulan 

 Expedition between Lat. 45° 57', Long. 6° 41', and Lat. 46° 40', Long. 

 6° 58' in 400 to 1700 metres. Koehler remarks (6) that all these 

 specimens are identical with those from the coasts of Norway. 



Bell (1) makes the translucency of the arm spines the key of the 

 species, and this characteristic and the moniliform appearance of the 

 arms is very marked in the Hiixlcy specimens. 



Grieg (3) remarks that 0. abyssicola seems to be subject to sundry 

 small variations as regards the spines on the disc, the aculeation of 

 the branchial spikes, and their number, which is variable, and should 

 not, in his opinion, be regarded as specifically diagnostic. 



The spinulation of these young specimens is w^orthy of note. Both 

 the dorsal and ventral surfaces of the disc are covered with thin sub- 

 circular imbricated scales. All the dorsal scales bear a knob or 

 granule crowned with two to six very fine thorns. These thorny 

 knobs are not present on all the ventral scales. As the disc increases 

 in size the thorns grow longer, but the basal knob or granule remains 

 about the same size. As the disc increases in size the thorns appear 

 to coalesce into a single longer aculeated spine. This spine is much 

 constricted at the proximal end, and easily breaks off from the knob. 

 In the adult probably all the longer spines ultimately break oh", 

 leaving the disc covered with knobs or granules, as figured by Grieg- 

 I have observed similar changes in Ophiactis Balli, and they are prob- 

 ably common to other Ophiurids. 



