20ß 



K. MITSUKUllI : STUDIES ON 



extended. Moreover, when we look at them from inside, the 

 vesicles which are present on the inside, corresponding to each of 

 the dorsal papilla?, are arranged in two rows, one on each side of 

 the ambulacrum. The length of the papillae is, in preserved 

 specimens, 0.7 — 1 cm. The lacuna? in the ventral perisome, cor- 

 responding severally to each lateral pedicel and its three divisions, 

 are similar to the structures described in Lcdmogouc violacea. 



In tiie dorsal perisome, there are present large wheels, with 

 small wheels only in very small proportion, if present at all ; 

 some of the former arci the largest in the whole body. They 

 have mostly nine spokes (rarely eight, ten, eleven or twelve, 

 sometimes even sixteen) and six central holes (very rarely four, 

 seven or eight) ; the diameter measures 0.06 — 0.255 mm., but 

 commonly 0.10 — 0.18 mm. In dorsal papilla?, the basal part has 



large and small wheels, 

 but toward the upper part 

 only small ones are pre- 

 sent. The small wheels 

 have the margin cre- 

 nate ; spokes eleven or 

 twelve, central holes four, 

 diameter 0.030 — 0.048 

 mm. 



While we may find 

 large " large wheels " in 

 small individuals and 

 small " large wheels " in 

 large individuals, there is 

 in many cases a striking 

 contrast in appearance be- 



Textfig. 37. 



Uyodoiiion Ijhuai : a — Calcareovis 

 ring ; b — Lurge wheel of dorsum ; 

 c — Small wheel ; d — Supjx>rling 

 rotl. (b—dx2iM)). 1-Iaterradia,li:i; 

 K — Had i alia. 



