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



broad, and thick, meeting well within, where they are slightly narrower than without. 

 First under arm plate small, nearly square, with all four angles rounded ; the next 

 two larger, pentagonal, with an angle inward, outer lateral corners rounded, and deep 

 re-entering curves on the lateral sides, where the tentacle scales stand ; the under 

 arm plates beyond these are minute and triangular, having an angle inward and the 

 outer edge slightly curved. Side arm plates large, swelling without into a rounded 

 ridge and forming the greater part of the covering of the arm. Upper arm plates 

 triangular, with an angle inward, and all three sides slightly curved. Disk massive and 

 flat, covered with thick, slightly swollen plates, one pentagonal primary in the centre, 

 surrounded by five rudely hexagonal plates ; interbrachial spaces filled by one hexagonal 

 plate within, and a smaller quadrangular extending to the very large marginal plate, 

 which is much swollen and has a constriction on the outer edge. Eadial shields large 

 and angular, wider without than within, with outer angles rounded, separated their entire 

 length within by an hour-glass shaped wedge of three small plates. Lower interbrachial 

 space covered by the great marginal plate, the broad genital scales extending from the 

 mouth shield to the marginal plate, and by three intermediate plates. There are two 

 short blunt arm spines, besides a supplementary spine on the top of the side arm plate. 

 Tentacle pores at the second and third under arm plates only, with one small round scale 

 on each pore. Colour in alcohol, greyish. 



By its general shape, and by the extra spines on top of the arm, this species 

 approaches Ophiomusium acuferum, but is distinguished by form and arrangement of 

 disk plates. It is covered by a well-marked skin, to which often adhere numerous 

 Globigerinas. The supplementary arm spines do not go beyond the third joint from the 

 disk and are often missing. 



Station 192.— September 26, 1874 ; lat. 5° 42' S., long. 132° 25' E. ; 129 fathoms; 

 mud. 



Ophiomusium validum, Ljn. (PI. I. figs. 1-3; PI. XXXIX. figs. 11-13). 



Ophiomusium validum, Ljn., Dr. Goes, Opli. Of. Kong. Akad.. p. 618, 1871 ; Bull. Mus. 

 Zool., vol. v., part 7, p. Ill, pi. i. figs. 7-9; Bull. Mus. Comp. Zool., vol. v., part 9, 

 p. 219. 



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. Four 

 small, equally spaced arm spines. Smaller upper arm plates. The great lower inter- 

 brachial plate has usually two much smaller at its outer corners. 



(Type specimen from Station 24.) Diameter of disk 8 "5 mm. Width of arm, with- 

 out spines, close to disk 2 mm. Mouth papillae five on each side, with a large diamond- 

 shaped one at angle of jaw, all forming a close line. Mouth shields large, irregularly 



