466 Prof. P. M. Duncan and Mr. W. P. Sladen on 



although it differs slightly from the type form in the relative 

 measurements of certain points of detail, we have little hesita- 

 tion in assigning to Dr. Llitken's species, the variations, in our 

 opinion, not being of greater importance than such as we 

 should regard as dependent on locality and conditions of life. 



The arms are less broad, and take their origin in a more 

 deeply reentering curve of the disk-rnargin, the radial shields 

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

 tion to their length is less than in the type forms, as the fol- 

 lowing 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.JiUformis ; 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. 



OjpMacantha spinulosaj Miiller and Troschel. 



? Asterias bidentata, Retzius, Diss. p. 33. 



? Ophiura fragilis, Sabine in Append. Capt. Parry's Voyage. 



? Ophiocoma hidentata^ Miiller & Troscliel, Syst. d. Asteriden, p. 99. 



Ophiacantha spimdosa, Miiller & Troschel, Syst. d. Asteriden, p. 107. 



O. grcenlandica, MiiUer & Troschel, Archiv fiir Naturgesch. 1844, 



p. 183. 

 Ophiocoma arctica, Miiller & Troschel, Sj'st. d. Asteriden, p. 103. 

 O. echinulata, Forbes, Append. Sutherland's Journal. 

 Ophiacantha sjnnulosa, Liitken, Add. ad Hist. Ophiuridarum, p. 65 ; 



Lyman, 111. Cat. Coinp. Zool. i. p. 93; Ljungman, Oph. Viventia, 



(Efv. K. Vet.-Akad. Forh. 1866, p. 326. 



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

 Fraser, 80 fms. ; Franklin-Pierce Bay, 15 fms. Temperature 

 29°-5 Fahr, 



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

 stony. 



