560 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The orals are triangular, the proximal j^ortion in the shape of a spherical 

 triangle, along the two free sides of which the borders are abruptly everted, the 

 eversion increasing in amount to the apex and standing everywhere in planes 

 including the dorsoventral axis. 



Similar eversion of the free borders of the orals was described in Antedon 

 bifida by Dr. W. B. Carpenter, but it is not nearly so extensive as in this species. 



Along the base of the triangle, where the oral adjoins the corresponding basal, 

 there is a narrow belt of regularly arranged holes representing the zone of new 

 growth. It is much narrower than the same zone in the basals. 



Five sacculi are present. 



In the next stage, characterized by the presence of the radials, the length is from 

 6 mm. to 8 mm., of which the column occupies from 5 mm. to 7 mm. and the calyx 

 0.7 mm. to 0.8 mm. 



The number of the columnals is 22-24. The longest, the eighth-fourteenth, 

 are cylindrical, with the median annulus distinct, though scarcely prominent, and 

 measure 0.05 mm. by 0.005 mm. The distal columnals are somewhat shorter, and 

 the three or four proximal quite short, only slightly wider than those succeed- 

 ing. The terminal stem plate is distinctly lobed. 



The radials are represented by small rhomboid plates lying in the angles where 

 the basals and orals meet, the corners of these plates being truncated for their 

 reception. 



The basals have increased considerably in length through addition to their 

 distal borders. There has been some addition to the proximal edges of the orals, 

 and their everted margins have increased considerably in height. 



The tentacles contain irregular elongated calcareous rods. 



A specimen in which the rudiment of the IBr^ has appeared shows the begin- 

 nings of the radianal. The right posterior radial is displaced to the right so that 

 it lies almost entii-ely on the right posterior basal. Adjoining it just to the left 

 and resting on the posterior basal is the radianal. In area the radianal is some- 

 what more than one-third the area of the adjacent radial, and its distal half 

 overlaps the base of the posterior oral when the latter is closed over the disk. 



In the stage in which the IBrj and IBrj are developed the length is 8.5 mm., 

 the calyx being from 0.7 to 0.8 mm. long. 



There are 25 columnals, of which the longest are 0.5 mm. long and from 0.06 

 mm. to 0.07 mm. wide, somewhat thicker than in the preceding stage and slightly 

 thickened at the ends. The lobes of the terminal stem plate have become slightly 

 more pronounced. 



In one of the specimens the IBri and IBr, are small and similar; in another 

 they have become considerably differentiated. 



In the latter the IBr, is still narrow and slender, though somewhat widened 

 at the proximal end, where it adjoins the now distinctly i^entagonal radial. The 

 IBrj (axillary) has widened, and on its outer borders the first brachials have just 

 appeared. 



The basals have increased considerably in length through addition distally, 

 and the radials have nearlv come into mutual contact bevond them. 



