Agelacrinidae and Lepadocystinae 409 
to 'the underlying surface. The plates belonging to the two outer 
rows of the inner part of the peripheral band are characterized by 
the presence of three short ridges. These ridges are found near 
the basal margins of the plates. In length they vary from four- 
fifths of a millimeter to less than half a millimeter; and they are 
equally spaced, the three occupying a width of four-fifths to one 
millimeter. In direction they vary from approximately vertical 
to moderately radiating in an upward direction. They fill in the 
spaces between the adjacent plates belonging to the next inner 
circle of large plates forming the inner band. They may be merely 
space fillers, assisting in holding these plates of the inner band 
rigid, but they may also be points of attachment for muscles. They 
do not fit into grooves on the distal faces of the adjoining plates of 
the inner band. These ridges were noted by Meek, presumably in 
a specimen of Agelacrinus faheri, identified by Meek as Agela- 
crinus cincinnatiensis , found by L. B. Case in the upper part of the 
Richmond group, at Richmond, Indiana. This specimen seemed 
to have grown on a valve of Byssonychia, and exposed the under 
surface of the oral face of the theca. Regarding this specimen 
Meek stated: ^^The disc plates near the outer margin show, on 
their inner surfaces, little parallel ridges, directed inward, and 
apparently fitting into corresponding furrows in the lapping edges 
of the contiguous pieces.’’ I doubt the presence of this corre- 
sponding furrows but have not seen the specimen. On specimen 
13266-1-s, (plate I, Fig. 6D), belonging to the American Museum 
of Natural History, there are two thecae of Agelacrinus pileus. 
Of these, one is considerably dismembered and exposes the inner 
surface of two of the plates belonging to the inner band of the 
peripheral ring. Here, again, short vertical ridges, 0.4 mm. in 
length, project from the lower margin of the plate. On one of 
these plates the vertical ridges occupy a total width of 1 mm.; on 
the other, of 1.3 mm. They evidently never fitted into grooves in 
the next inner set of plates. 
13. Central Part of Aboral Surface 
No definite information has been secured regarding the central 
part of the aboral surface of the theca, within the space limited by 
the peripheral ring. Possibly the under side of the oral face of 
the theca of Agelacrinus pileus, figured by Miller and Faber, No. 
