EEPORT ON THE OPHIUROIDEA. 367 



space on each side. IV'low is the arm bone, 

 with its under (h) and side arm phites {i) bear- 

 ing the spines. On either side passes up the 

 genital opening {no) into the bursa with its 

 folded wall which closely follows the pleated 

 digestive cavity (St, St), with its thick (hepatic, 

 or epthelial ?) layer. One little lobe {St') is 

 pushed into the bursa and cut liy the section. 

 The wall of the bursa is a thin continuation 

 of the disk wall ; hence its tendency to calcify. 

 In this species it has fine scales of lime in its 

 .sul)stance. In the bursal folds lies a young 

 (Y) ; and two embryos (Y') are seen in side 

 pouches. To the right of the upper arm of 

 the young may be seen a section of a tip of 

 another arm, bent round in a fold of the bursa ; 

 genital plate (o) ; tentacle (r) ; radial shields 

 cut through (1,1). 

 Fig. 9. Ophiacantha vivipara, Ljn., $ , ^f. Liver-like cells from the very thick wall 



of the digestive cavity. This layer seems to be 

 the one spoken of l»y Ludwig as epithelial. 



PLATE XLVII. 



Fig. 1. Astroj^hyton exiguum, Agas., f-. Disk from above, with two arms. 



,, 2. OphiogIi/2)ha hexactis, E. A. Smith, $ , f . Disk with its roof removed and seen 

 from above. Above the digestive cavity {St, St), which is ruptured in 

 the middle, lie the genital bursse {§S), near which may be seen four young 

 ones in several stages of growth. Each is contained in a translucent 

 membranous sac, W'hich is ruptured over the largest. 



„ 3. Ophiocoma scolopendrina, Agas., $ , f. Vertical section of the disk passing 

 through one arm {Am) and the opposite interbrachial space: digestive 

 cavity {St), whose upper wall adheres to the roof of the disk ; jaw (c) ; 

 section of mouth frame (/) ; genital plate {u) ; genital bursa (<5) ; con- 

 voluted spermaries (^',^'). 



,, 4. OpMotlmx longipjeAa, Miill. & Tr., $ , -f-. Vertical section of the disk passing 

 through one arm {Am) and the edge of the opposite interbrachial space, 

 including a slice of an arm {Am). The spaces over and beside the arms 



