36 



AET. 2. — H. MATSUMOTO 



well developed in every second or third joint, in which they bear 

 each a conspicuous, movably articulated tubercle at the upper end. 



Most specimens are quite 

 young and srnaller than 4 mm. 

 in the disk diameter. They 

 are mostly six -armed, rarely 

 five or seven-armed. On the 

 upper side of each arm joint, 

 there are two transverse rows 

 of rough, skin-covered nodules, 

 six to eight in each row. 

 Similar nodules occur on the 

 radial ribs ; and in the larger 

 specimens they are also found 

 on the joints of the slender 

 parts of the arms. 



I have also some six- 

 armed specimens, in which 

 the middle one of the three 

 regenerating arms is distinctly 

 smaller than the other two ; 

 but I do not agree with 

 Clark in looking upon the 

 smaller arm as being destined 

 for resorption, so that the 

 animal would become five-armed. The smaller size of the arm in 

 question is perhaps due to its unfavourable position with regard 

 to the supply of nutrition. In fact, we see in many ophiurans 

 which reproduce by schizogony, that the regenerating arms do not 

 often keep to the original number, and tlie same occurs also in 



Fig. 7. Astroceras ■pergamemt. a. From above. 

 X 7. h. From above, x 8. c. From be ow. x 14. 

 h and c. Young. 



