318 ART. 2. — H. MATSUMOTO. 



Ophiarachna incrassata (Lamarck). 



Opldura incrassata : Lamarck, Hist. Nat. Anira. saus ^''ert., II, 1816, 

 p. 542. 



Ophiarachna incrassata : Müller & Troschel, Sys, Ast., 1842, p. 

 104 ; LÜTKEN, Addit. Hist. Opli., Ill, 1869, p. 33 ; Lyman, Bull. Mus. 

 Comp. ZooL, III, 1874, p. 221 ; Lyman, Kep. Challeuger, V, 1882, p. 173 ; 

 Brock, Zeitschr. wiss. Zool., XLYH, 1888, p. 495 ; Kœhler, Exp. Siboga, 

 XLV, Pt. 2, 1905, p. 64 ; Kœhler, Bull. Sc. Fr. Belg., XLI, 1907, p. 330 ; 

 Clark, Bull. Mus. Comp. Zool, LI, 1908, p. 298; Clark, ibid., LH, 1909, 

 p. 128. 



Three specimens ; Bonin Is. One specimen ; Okinawa. 



Indo-Pacific. Okinawa and Bonin Is. seem to be the northern 

 limits of this species. 



One of the specimens from the Bonin Is. and the one from 

 Okinawa agree perfectly with Müller à Tkoschel's description. 

 The largest one from the Bonin Is. is 50 mm. in the disk diameter, 

 170 mm. in the arm length and 8 mm. in the arm width at base. 

 Its colour in alcohol differs from that of the others, and is yellow- 

 ish brown above, dark brown below, being handsomely dotted 

 with lighter shade on the ventral interbrachial spaces, on the oral 

 shields, on the tentacle scales, and on the lower arm spines. The 

 tliird specimen from the Bonin Is. is notably different from the 

 others : the oral shields are a little lonsrer than wide, and the 



the tip of the oral angles ; cluster of dental iJapillœ j)resent ; dorsal arm plates very narrow, so 

 that the arm spines more or less approximate dorsaUy in a few basal arm joints; ventral arm 

 plates entirely seiDarated from one another ; arm spines extremely long, translucent and finely 

 serrate ; single tentacle scale to each pore (two scales to the first pore only), not overlajiping 

 the base of the lowest arm spine. 



All the distinctive characters of Ophiurochœta are perfectly Ophiodermatine, and those of 

 the type of OpJdoireta thoroughly Oi>hiaeanthine. I believe that, Ophiurochœta cannot be united 

 \\ith Ophiotreta, unless the majority «jf the now recognised genera of the Ophiuroidca should be 

 united to a single gentis. 



