212 THE VOYAGE OF H.M.S. CHALLENGEE. 



space two genital openings, beginning close outside the moutli shield. The peristomial 

 plate is in three pieces, arranged symmetrically like the mouth shield and side mouth 

 shields. 



Although strongly resembling Ophiacantha and OiDliiomitra in outward aspect, this 

 genus has a peculiar internal structure. In the first place there is no genital scale, and 

 the genital plates, instead of occupying their usual position at the side of the arm, lie on 

 top, side by side and touching each other. They are long, bar-like, and a little curved, 

 and narrowest at their outer end (PI. XLII. fig. 1, o). Then the ovarial bursse have 

 their walls clad in thin lime plates, making a regular wall in which I was unable to 

 discover a genital opening of any sort (8). The peristomial plates are of great size, 

 completely covering each mouth angle, except its inner apex. They are in three pieces, 

 two forming an angle, whose opening is closed by the third ; the three resembling a 

 mouth shield with its two side shields {v,v). The radial shields are large and wide, and 

 touch each other for nearly their whole length. 



See Plate XLII. fig. 1. 



Ophiotliamnus vicarius, Lym. (PI. XLII. fig. 1). 



Ophiofhamnus vicarius, Lym., Bull. Mus. Comp. Zool., vol. i., part 10, p. 342, 18G9 ; 111. Cat. 

 Mus. Comp. Zool., No. vi., pi. ii. figs. 8, 9, 1871 ; Bull. Mus. Comp. Zool., vol. v., part 7, 

 p. 150; Bull. Mus. Comp. Zool., vol. v., part 9, p. 232. 



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



Ophiothamnus remotus, Lym. (PI. XIV. figs. 1-3). 



Ophiothamnus remotus, Lym., Bull. Mus. Comp. Zool., vol. v., part 7, p. 149, pi. viii. figs. 

 201-203, 1878. 



Disk scales coarse and angular. Side mouth shield very large, and meeting broadly 

 within. Very few short spines on disk. 



(Type specimen from Station 142.) Diameter of disk 3 '3 mm. Length of arm 11 mm. 

 Width of arm without spines 8 mm. Seven flat close-set mouth papilla3 ; the odd 

 one, at the apex, being short sj^earhead-shaped, the rest squarish. Mouth shields small, 

 three-sided, with a point inward, and the outer corners rounded ; length to breadth 

 •4 : '3. Side mouth shields very wide and large, meeting broadly within, and enveloping 

 the mouth shield on all .sides but one. First under arm plate small and wedge-shaped, 

 with inner end rounded ; the rest are pentagonal, with an obtuse angle inward, and outer 

 corners somewhat rounded ; the second plate is larger than those beyond. Side arm 

 plates meeting broadly above and below, constricted within, swelling outward into a 

 thickened spine ridge. Upper arm plates mder than long, irregular oval, with a slight 

 peak within. Disk rather thick, covered above with coarse angular scales, whereof there 

 are but two radiating rows in each interbrachial space ; radial shields wide pearseed- 



