ASTEROIDEA 209 



sense organ (PI. XVI, figs. 6-8). It is deeply hollowed on the actinal face, and the border 

 of the distal half carries, on either side, 6-8 acicular spines which support a fleshy 

 cushion of tissue (coalesced sacculi) thickly beset with pedicellariae. In the young, this 

 compound sacculus appears very early and its pedicellariae are the first to be developed, 

 indicating the importance of the terminal sense organ (PI. XVI, figs. 9-1 1). The form and 

 relative size of the sense organ are indicated in the figures. 



In fully developed specimens papulae occur on the disk, as indicated above ; on the 

 dorsal surface of the genital region, irregularly according to the skeletal meshes, 

 dwindling to i or 2 dorsally in intercostal spaces VI or VII ; on the lower part of inter- 

 costal spaces I to VI where, in the type, space I has 2 or 3 ; II and III have 5 or 6 each; 

 IV has 2 (but numerous ones on dorsolateral region); V has i ; VI has i or o. In the 

 medium-sized specimen figured (PL XVI, fig. 3) only the first 3 spaces have papulae in 

 this position. The dorsal and dorsolateral papulae are omitted to avoid confusion of lines. 

 Apparently the papulae never encroach upon the upper part of the intercostal space I. 

 In a specimen (St. 123) having R 18 mm. (PI. XVII, fig. 2) I can find no papulae. In a 

 specimen with R 37 mm. (St. 172) papulae have appeared sparingly in a marginal zone 

 on disk, dorsally on the short, developing genital region, and ventrolaterally in inter- 

 costal spaces I and II (i papula to each) (see also Growth stages, 4). 



Intercostal space I, in the female, becomes the side of the nidamental cavity and, with 

 the growth of the young, is forced inward to the sagittal plane until it presses against the 

 similarly stretched wall of the other side of ray. The hepatic coeca occupy the arched 

 upper portion of the swollen genital region and their connection with the stomach is 

 through the very constricted opening of the base of ray (PI. XVI, fig. 4). The already small 

 aperture afforded by the first skeletal arch is further decreased by a membranous 

 diaphragm in the dorsal part of the first arch, as indicated in the figure. In fully grown 

 specimens this diaphragm is even more extensive than in the figure and the passage to 

 ray is correspondingly smaller. 



The general facies of actinal surface is well shown by the photograph. The adam- 

 bulacral plates, short at base of ray and gradually becoming longer and lower as is 

 characteristic of Brisingids, bear each a single acicular spine on the actinal surface. This 

 spine is similar and subequal to the lateral spines at base of ray, but soon the latter are 

 decidedly the longer. It carries a lateral flap of tissue covered with pedicellariae and the 

 tip of the proximal spines is not in the least degree modified. No furrow spinelets present. 

 The first adambulacral plate remains on the disk when a ray breaks oflt. The joint 

 between the first and second plates is a muscular one, not different from the preceding 

 nor the third and following ones, except that the muscular space widens slightly as the 

 flexible portion of ray is reached. At each mouth angle the first pair of adambulacral 

 plates is tightly apposed by the lateral face, and the second pair to a less extent, that part 

 which is involved being indicated by dots in PI. XVII, fig. 5. Above the first united pair 

 of adambulacrals is a pair of small inferomarginals forming a part of the disk skeleton ; 

 while above adambulacrals 2 and 3 is inferomarginal 2 (PI. XVI, fig. 5), a portion of the 

 lateral face of which (dotted) is joined to its fellow of the adjacent ray. 



