REPORT ON THE OPHIUROIDEA. 89 



shields long, triangular; much wider without than within, where they do not quite 

 meet. Genital scales concealed under fine, closely-set disk scales. Under arm plates 

 pentagonal near base of arm, farther out quadrangular, with an angle inward ; one 

 tentacle scale which is round, and situated on inner angle of the second and third 

 under arm plates. Side arm plates thick, minutely tuberculous, meeting below, but 

 not above, near base of arm. Upper arm plates near base of arm hexagonal, with outer 

 and inner sides very short. Disk covered above and below by thin, rounded, minutely 

 tuberculous scales ; on the margin are larger angular plates of the same character. 

 Radial shields small, minutely tuberculous, rounded triangular ; length to breadth 

 1'5 : "7 ; widely separated by a group of half a dozen plates, of which the outer ones are 

 much wider than long. Two or three minute peg-like arm spines situated in a notch 

 low on the side arm plate. Colour in alcohol, pale grey. 



Station 33. — April 4, 1873; off Bermudas; 435 fathoms (same species?); mud. 

 Station 236.— June 5, 1875; lat. 34° 58' N., long. 139° 30' E. ; 420 to 775 fathoms; 

 mud. 



Ophiomusium archaster, Wyv. Thorn. (PI. II. figs. 4-6). 



Ophiomusium archaster, Wyv, Thorn., MS. ; Lyin., Bull. Mm Corap. Zool., voL v., part 7, p. 

 112, pi. ii. figs. 28, 29, 32, 1878. 



Arms rather slender and tapering, cylindrical, or but slightly wavy. Upper and 

 under arm plates persisting nearly to end of arm, but no tentacles beyond third or fourth 

 under plate. Genital opening bounded by small close-set papillae. Disk covered by 

 thick skin, its upper surface occupied chiefly (and in half-grown specimens almost 

 entirely) by radial shields and large primary plates, with small scales between. Arms 

 even and cylindrical. Four minute rudimentary arm spines. 



(Type specimen from Station 323.) Diameter of disk 10 mm. Width of arm 

 close to disk, without spines, 2'5 mm. Five mouth papillae on each side, short, 

 pointed, closely joined with one large, diamond-shape at angle of jaw. Mouth 

 shields broad, heart-shaped, with a peak within; length to breadth 1"3:1*5. Side 

 mouth shields long triangular, very broad without ; tapering and curved inward where 

 they meet. First under arm plate very small, triangular, with angle inward ; the 

 three next bear tentacle scales, and are three-sided, with lateral sides a little re- 

 enteringly curved, and outer side slightly curved ; the rest are small, triangular, with 

 outer side curved. Side arm plates thick, slightly swollen, somewhat constricted 

 within, meeting below throughout, and above beyond the third upper arm plate. 

 First two upper arm plates rounded and much wider than those beyond, which are 

 triangular, with an angle inward, lateral sides straight, outer edge much curved. 

 Disk flat, covered with thick, minutely tuberculous plates and scales. Radial shields 



(zool. CHALL. EXP. — PART XIV. 18S2.) ' ' 1 - 



