REPORT ON THE OPHIUROIDEA. 185 



projecting spine ridge Disk puffed, densely and evenly beset, with very short, stout, 

 conical spines, which to the naked eye seem nearly like large grains ; scales and radial 

 shields entirely covered. Eleven stout, blunt, regular, cylindrical arm spines, which, 

 under the microscope, are slightly rough. Lengths to that of an arm joint, 3 "5, 47, 4, 

 3-8, 3'8, 2'8, 2-5, 2'5, 2-5, 1*2, *8 : 1*3. One very large, thick, pointed tentacle scale, 

 over 1 mm. long. Colour in alcohol, pale rose-pink above ; below yellowish. 



Specimen from the distant station 145 differed only in having larger spines on the 

 disk. A young one, with a disk of 7 mm., had only seven mouth papillae to each angle ; 

 the additional papillae at the outer end of mouth slit had not yet appeared ; the disk 

 spines were forked and thorny, and the eight arm spines were rough, and almost thorny. 



Station 145.— December 27, 1873 ; lat. 46° 40' S., long. 37° 50' E. ; 310 fathoms. 

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

 Station 308.— January 5, 1876; lat. 50° 10' S., long. 74° 42' W., 175 fathoms; mud. 



Ophiacantha vivipara, Ljn. (PI. XLVI. figs. 7-9). 



Ophiacantha vivipara, Ljn., Om Tvanne Kya arter, Of. Kong. Akad., p. 471, 1870 ; Lym. 



Bull. Mus. Comp. Zool., vol. v., part 7, p. 149. 

 OpMocoma (?) vivipara, Wyv. Thorn., Voyage "Challenger," Atlantic, voL ii. p. 242, fig. 50. 



As its name indicates, the species has always been known as viviparous. 1 It carries 

 its young, until they are quite large, in the ovarial bursa (PI. XLVI. fig. 8, Y), whence 

 they often thrust an arm through the genital opening (no.). Plainly this is a mode of 

 reproduction differing greatly in degree from that of the egg-laying species, where we 

 find the ovarial tubes crammed with thousands of small ova. In the viviparous there is 

 no room for such numbers, because the young become so large that a few of them occupy 

 the entire cavity. They are evidently produced in a series. The vertical section at a 

 right angle to an arm, cited above, shows, besides the large young, two embryos in 

 pockets (Y', Y'), ready to take the place of the larger brood when it quits the mother. 

 The bursa? are pleated bags having lime scales in their substance and adhering to the 

 thickened wall of the digestive cavity (St). They pass upward over the arms ; but do 

 not force themselves between the roof of the disk and the digestive cavity, for the upper 

 wall of the latter clings pretty closely to the roof and the under side of the radial shields 

 (I, I.). A parallel cross cut made close to the edge of the disk (fig. 7) shows two of the 

 bursas (S,S.) as simple cracks passing upward, and having between them a lobe of the 

 digestive cavity (St) which lies just over an arm. The third bursa (S') has genital tubes 

 or pockets, which lie over an arm. This section exhibits also one brachial and two 

 intcrbrachial lobes of the digestive cavity, with their very thick pleated walls. A 

 portion of these, highly magnified (fig. 9) showed rows of elongated oval cells, with long 

 thread-like, or fibrous, or tubular prolongations, the whole resembling the liver cells of 



1 Ljungman, loc. cit. ; Wyv. Thomson, he. cit. 



