408 
Aug. F. Foerste 
closely to secure support. It is inconceivable that this close 
application of the margin of the peripheral ring could be accom- 
plished if the latter were underlaid by imbricating scales. There- 
fore, imbricating scales are believed to have been absent at least 
from that part of the aboral surface which underlaid the margin of 
this ring. 
11. Rigid Inner Band of Peripheral Ring 
In agreement with the ready mobility of the marginal part of 
the peripheral ring, this part is covered with small imbricating 
plates arranged in diagonal rows. These increase in size toward 
the inner part of the peripheral ring, forming an inner band of 
strong plates, usually elongated transversely, or at least so imbri- 
cated as to expose only the wide upper margins of the plates. This 
inner band of large plates rarely has suffered deformation, suggest- 
ing that here the plates were held together more or less rigidly. In 
fact, while the interambulacral surfaces frequently are found 
sagged below the level of the inner margin of this peripheral band, 
after the death of the animal, and while even the distal parts of 
the rays not infrequently give evidence of sagging (see, for in- 
stance, Fig. 1, on plate II), the inner band of the peripheral 
ring usually retains its form. It remains undisturbed even in 
specimens in which almost all the interambulacral and ambu- 
lacral plates are disarranged. The surfaces of these plates of 
the inner band of the peripheral ring usually are closely applied 
to each other, forming a rigid circle of plates. 
12. Vertical Ridges on Plates of Inner Band of 
Peripheral Ring 
In a specimen of Agelacrinus belonging to the American Museum 
of Natural History, forming No. 13266-1-r of that collection 
(plate I, Fig. 6E), the under side of the upper or oral face of the 
theca is exposed. The species is assumed to be Agelacrinus pileus 
on account of the strong convexity of the theca, and its compara- 
tively small diameter: 20 mm. This specimen suggests that not 
only all of the smaller plates belonging to the marginal part of the 
peripheral ring, but also the lower margins of the outer two rows 
of the inner band of much stronger plates, could be brought close 
