280 



THE VOYAGE OF H.M.S. CHALLENGER. 



bag, where they go through a pore into the liursa, which is merely a lobecl indentation 

 of the disk wall, and is even somewhat coloured on the inside. In that respect it is not 

 quite like the bursa of most Ophiurans, which is composed of the lining memljrane, or 

 layer, of the body wall. 



The spermatozoa of OjMocreas (xdipus after their long immersion in alcohol, were 

 doubtless much altered. Strongly magnified, they resembled little translucent grains of 

 boiled sago, but showed no projection or ciliary tail. 



In fig. 1 , the floor of the digestive cavity {St, St) is slit to expose the spermatic 

 pouch, so that the lower portion is separated from the upper one, which lies under the radial 

 shield {I), and whose roof grows closely to the disk wall, as in Astrophytons. It also 

 adheres, as mentioned above, to the interbrachial floor of the disk wall. Indeed, it is 

 scarcely free at any point save a space along the top of the arm, which forms an oblong sinus. 



The interior of the digestive cavity is lightly marked by radiating pleats, and there 



are also five pairs of strong radiating ridges, a pair over each arm, which form partial 



partitions. 



Table of Species or OpMocreas. 



Diameter of 



Disk to length 



of Arm. 



1:19 



1 :21 



1:12-18 



1:13 



l:7i 



kSkiu sinootli, thin, and tight. Towards middle of arm, 

 lower tentacle scale as long as two joints, and a little 

 clubbed. Radial shields slender but meeting in the 

 centre. Side arm plates stout, and at base of arm 

 joined to well-marked under arm plates, while the 

 upper arm plates are rudimentary. 



Skin .smnoth, thin, and tight. Lower tentacle scale (which 

 is shorter than in O'lihiocncvi luiiibricu-v) enclosed in a 

 club-ended skin bag. Radial shields feeble and not 

 meeting in centre. But side arm plates very stout, 

 and joined to thick upper arm plates. Under arm 

 plates well marked. 



Skin very thick, loose, and wrinkled. Tentacle scales 

 short and not club-ended. Side arm plates meeting 

 below and joined to thick, crust-like, upper arm plates. 

 Basal under arm plates well marked. 



Skin thick and a little puffed on arms. Tentacle scales 

 cased in thick skin bags ; and nearly as long as in 

 Ojihiocreas Jtimhricv.<i. Mouth angles swollen so as 

 nearly to fill the mouth, as in OpJu'ucreas curmisuti. 



Skin soft and moderately thick. Tentacle scales .short ; the 

 lower one longer, but scarcely club-ended. Side arm 

 plates like little mamelons. No upper arm plates. 



Oph iocreas Jiimbrictut 



Ophiocreas cedipus. 



Opiiiocreas carnostis, 



OjjMocrcas caudatus. 



Ophiocreas ahysi^icola. 



Note. — The arm plates, mouth shields, &c., can only be seen by removing the skin. 



