86 THE VOYAGE OF H.M.S. CHALLENGER. 



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 papilla?. Inter- 

 brachial space between radial shields occupied by two large plates. Papillae along 

 genital openings extending upward as a small arm comb. Four or five small arm 

 spines. 



(Type specimen from Station 23.) Diameter of disk 10 mm. Width of arm near 

 disk, without spines, 2 - 5 mm. Mouth papillae six on each side, with one at angle of jaw, 

 all in close contact. Mouth shields heart or rounded diamond shape, with an angle inward ; 

 leno-th to breadth 1*5 : 1. Side mouth shields Ions; triangular, extending farther out than 

 the mouth shield ; wider without than within, where they just meet. The first four under 

 arm plates bearing tentacle scales are pentagonal, with an obtuse angle inward, outer edge 

 slightly curved, lateral sides re-enteringly curved ; length to breadth, second arm plate, 

 *1 : - 7. Side arm plates thick, constricted within, meeting below, even within the disk, 

 and above, beyond the second upper arm plate ; those beyond are also pentagonal, but 

 small, broad, and widely separated. Upper arm plates triangular, with an acute angle 

 inward, and outer edge curved ; length to breadth 1:7. Disk covered with fiat plates 

 closely soldered ; in the central space within the radial shields are six rounded primary 

 plates, separated by a circular row of small ones ; the interbrachial space is occupied by 

 two angular plates, the outer one much larger. Radial shields long triangular, separated 

 their entire length by one small and tw r o large scales. In the interbrachial space below 

 are two large circular plates, extending from the mouth shield to margin of disk, on 

 either side of which are smaller circular scales. Genital scales long and very narrow, 

 extending from the edge of the mouth shield to margin of disk, on the free edge of 

 which are fine tooth-like papilla?, corresponding to similar papilla? along the side mouth 

 shields, giving a resemblance to Ophioglypha. At the base of the arm above are short, 

 blunt papilla? on either side of first upper arm plate. Arm spines four or five, delicate, 

 pointed, nearly equally placed ; middle one longest and nearly half as long as a side arm 

 plate. A single circular tentacle scale on second, third, and fourth under arm plates, 

 situated near the inner angle. The entire surface of the animal is microscopically tuber- 

 culated. Colour in alcohol, white. 



This species much resembles Ophiomusium eburneum, but I am unable to decide that 

 they are the same. 



Station 23. — March 15, 1873; off Sombrero Island; 450 fathoms; globigerina ooze. 



Ophiomusium armigerum, Lym. (PL II. figs. 7-9). 



Ophiomusium armigerum, Lym., Bull. Mus. Comp. Zool., vol. v., part 7, p. 109, pi. i. figs. 21, 

 22, 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 



