278 APPENDIX. No. IX. 



deeply re-entering curve of the disk-margin, the radial shields 

 are narrower, and the breadth of upper arm- plates in pro- 

 portion to their length is less than in the type forms, as the 

 following measurements will indicate : — Diameter of disk 8 

 millims. ; radial shield, length 1 *3 millim., breadth *35 

 millim. ; sixth upper arm-plate, length *6 millim., breadth 

 •9 millim. 



The spines are hollow cylinders, stout, blunt, and but 

 slightly tapering ; the upper spine on each side-plate tapers 

 most. The first fifteen arm-joints bear four spines, the suc- 

 ceeding joints three only. 



An interesting feature connected with this specimen is 

 worthy of record, and is one which does not appear to have 

 been noted by previous observers. The central spines are 

 more or less flattened throughout their whole length; and 

 at the tip compression has been carried to such a degree as 

 to form a thin and somewhat expanded head — a peculiarity 

 which is at once suggestive of a characteristic spine-appen- 

 dage possessed by A. filiformis ; and although in the specimen 

 under notice this structural feature is by no means so fully 

 developed as in that Ophiuran, it is still sufficiently marked 

 to impress upon the mind the near relationship of the two 

 species and the community of their descent — an hypothesis 

 which is also further strengthened by the association of both 

 the forms in more southern waters. 



Ophiacantha spinulosa, Miiller and Troschel. 



Coll. Feilden : Discovery Bay, 25 fms., hard bottom ; Cape 

 Frazer, 80 fms. ; Franklin Pierce Bay, 15 fms. Temperature 

 29°-5 Fahr. 



Coll. Hart: Franklin Pierce Bay, 13-15 fms., bottom 

 stony. 



An Ophiacantha with disk covered with small round scales, 

 each bearing a small short spinelet. Eadial shields very 

 obscure, sometimes quite covered. No disk-incision ; and the 

 dorsal membrane is prolonged over the base of the rays. 

 Mouth-shields twice as broad as long, irregular ovate. Side 



