REPORT ON THE OPHIUROIDEA. 93 



pentagonal, with an acute angle inward and outer edge straight ; length to breadth 

 2:17. Side mouth shields longer than broad, wider without than within ; outer ends 

 curved, touching by their narrow ends within. Genital scales large, semicircular, 

 stretching from mouth shield to margin of disk. There are only three under arm plates, 

 the first small and diamond-shaped, lying at outer end of mouth slit ; second and third 

 pentagonal, with an angle inward, and lateral and outer sides nearly straight. Side arm 

 plates thick, slightly swollen, and beyond the third under arm plate forming the entire 

 covering of the arm, with the exception of rudimentary triangular upper arm plates, 

 which do not extend to the tip of the arm. Disk rather flat, and covered by closely 

 soldered plates ; the upper surface is occupied by six primary plates, separated by many 

 smaller ones ; radial shields rounded triangular, with acute angle within ; outer edges 

 curved, strongly diverging inward, and separated by a triangular scale. In interbrachial 

 space are two angular plates, the outer one wide quadrangular and closely soldered to a 

 great marginal plate, which, with the genital scales, covers the interbrachial space on the 

 under surface of the disk. At base of arm above are four little plates, two central and 

 two lateral. Four short, blunt, and thick arm spines, situated low on the outer edge of 

 the side arm plate. Tentacle scales minute, rounded, situated on the inner angle of 

 second and third under arm plates. Colour in alcohol, pale grey. 



In presence of the many new species of Ophiomusium, it has been thought well to 

 give figures and a full description of this one. 



Station 24.— March 25, 1873; off Culebra Island; 390 fathoms; mud. Station 23. 

 — March 15, 1873 ; close to Sombrero Island ; 450 fathoms ; globigerina ooze. 



Ophiomusium simplex, Lym. (PL I. figs. 7-9). 



Ophiomusium simplex, Lym., Bull Mus. Comp. Zool., voL v., part 7, p. 115, pL i. figs. 10, 11, 



1878. 



Most of the lower interbrachial space outside the mouth shield is occupied by broad 

 genital scales and a great central plate. No under arm plates beyond the third. Two 

 minute arm spines set low down. Besides the great interbrachial plate below there are 

 three others along the margin. 



(Type specimen from Amboyna.) Diameter of disk 6 mm. Width of arm without 

 spines 1"5 mm.; length of arm 15 mm. Mouth papillae seven on each side, and one, 

 spear-head shaped, at angle of jaw, closely soldered together and forming a slightly 

 raised continuous line. Mouth shields little longer than broad, pentagonal, with acute 

 angle within, at the corners of which begin the genital openings ; outer side straight. 

 Side mouth shields short, wide, with curved sides meeting within ; length 1 mm. Genital 

 scales large, semicircular, somewhat swollen, running from lateral corners of mouth shield 

 to margin of disk. There are only two under arm plates besides the small semicircular 



(zool. chall. exp. — part xiv. — 18S2.) O 13 



