404 
Aug. F. Foerste 
with moderate curvature is suggested by the ontogeny of Agela- 
crinus cincinnatiensis. In this species, individuals less than 9 mm. 
in diameter usually have moderately curved rays with the distal 
part not parallel to the peripheral ring. Specimens 10 mm. in 
diameter have a small part of the distal extremity parallel to the 
ring. In successively larger specimens, a larger and larger part of 
the distal extremity becomes parallel to the peripheral ring, until 
in mature specimens, this feature becomes conspicuous. Similar 
derivation of curved rays from comparatively straight rays have 
been shown in the ontogeny of Agelacrinites hamiltonensis and 
Agelacrinites huttsi, by Clarke, in New Agelacrinites, plate 10, 
Figs. 6, 7, 8, and 9, in 1901. 
5. Cause of Reversal of Curvature of Right 
Posterior Ray 
The cause of the reversal of curvature from contrasolar to solar, 
of the right posterior(No. 5) ray is unknown. Any attempt to solve 
the problem must, for the present, again be a subject merely of spec- 
ulation. Possibly this reversal of curvature is connected with the 
orientation of the specimen. Even in the living state, the position 
of the animal on a slanting surface would tend to increase the ten- 
sion along the upper part of the margin and just within the adja- 
cent part of the peripheral ring. If, at the same time, the anus 
were dragged slightly downward and toward the left, the proximal 
part of the right ray (No. 4) being directed up the supporting slope, 
then the greatest tension would be on the upper, right hand side of 
the inner curve of the peripheral ring, possibly sufficiently below the 
distal part of the right posterior ray (No. 5), in young specimens, 
to loosen the contact between this part of the peripheral ring and 
the immediately adjacent part of the posterior or anal interambu- 
lacral area, and thus to admit of the curvature of the right pos- 
terior ray in a solar, rather than a contrasolar direction. 
In the case of Agelacrinus cincinnatiensis, such a drag of the 
anus downward and toward the left is suggested by the presence 
usually of several small plates along the upper margin of the anal 
pyramid, the proximal part of right ray (No. 4) being directed 
upward. In one specimen of Agelacrinus cincinnatiensis, No. 
13266“l~b, belonging to the American Museum of Natural His- 
tory, these small plates are specially numerous along the upper 
