The Echinoderm Fauna of South Africa. 335 



P.F. 18933. Southeast from Cape Agulhas, 36 40' S. X 2126'E., 

 200 fms. Gn. s. 15 specimens; adult. 

 Bathymetrical range, 91-1000 fms. 



OPHIOTRICHIDAE. 



This large, tropical family is fairly well represented around the 

 Cape, in view of the extratropical character of the region. There 

 are ten species now known, representing four genera. The six species 

 of Ophiothrix are more or less perplexing owing to the variability of 

 several of the species, and to the fact that specific limits in the genus 

 are not well worked out as yet. In some species, the colour pattern 

 seems to be the most reliable character while in other cases it seems 

 to be perfectly worthless. So too with the character of the spinelets 

 or thorny stumps on the disk; these may give reliable specific cha- 

 racters but as a rule they are not to be trusted. The arm-spines 

 are usually dependable but their characters are not easily expressed 

 in words and they are not often distinctive. The following key shows 

 how the South African species of Ophiotrichidae may be distinguished 

 from each other, but in this family in particular such keys must be 

 used with caution. 



Key to the South African Species of Ophiotrichidae. 



Under arm-plates well developed. 



Disk plates with thorny stumps or spmelets or both ; these are often very 

 numerous, concealing the plates, but they may be few and scattered. 



Disk plates with numerous thorny stumps or rough spinelets or both. 

 Arm-spines, glassy, slender and sharp, though thorny 



Ophiothrix aristulata. 



Arm-spines more or less opaque, the longest ones at least, flattened 

 dorso-ventrally more or less, and truncate or blunt. 



Radial shields big and bare; rest of disk covered chiefly with 

 rough spmelets ; arm-spines little flattened Ophiothrix fragilis. 

 Radial shields smaller and usually more or less covered by the 

 small thorny stumps which occupy all the rest of the disk sur- 

 face; larger arrn-spines much flattened. 



Arms moderately long, 4 6 times disk-diameter; upper 

 arm-plates fan-shaped, rhombic or pentagonal, not much 

 wider than long, if any . . Ophiothrix triglochis. 



Arms very long, 9 18 times disk-diameter; upper arm- 

 plates very much wider than long Ophiothrix longipeda. 

 Disk plates with scattered acicular spinelets. 



Upper and under arm-plates obscured by skin ; five distinct radiating 

 black lines on disk, one extending onto base of each arm 



Ophiothrix capensis. 



