424 
Aug. F. Foerste 
one of the characteristics serving to distinguish the Ordovician 
species, usually referred to Agelacrinus or Lepidodiscus, from the 
typical Devonian species of these genera. The presence of two 
lateral covering plates on each side of at least all the larger floor 
plates has not been established as definitely as desirable, but this 
also may prove to be a characteristic of the unnamed Ordovician 
genus as compared with the typical Devonian representatives of 
Agelacrinus and Lepidodiscus. 
23. Anal Pyramid 
The anal pyramid of Agelacrinus cincinnatiensis is remarkably 
well preserved by specimen No. 13266--l"h, belonging to the Ameri- 
can Museum of Natural History. Here it consists of an exterior set 
of eight ovate plates, meeting at the center, and glimpses of three 
additional plates, belonging to the next inner circle. In specimen 
No. 13266-b, belonging to the same museum, there are also eight 
plates belonging to the outer circle of the anal pyramid, and more or 
less evident indications of eight plates belonging to the inner circle, 
and alternating with the outer circle. The plates of the inner 
circle probably were narrower than those of the outer circle, corre- 
sponding in this respect to the intercalated plates of the ambulacral 
cover series. The under side of the larger plates, belonging to the 
outer series of the anal pyramid, was ribbed longitudinally along 
the median line, so as to prevent displacement laterally, in this 
respect also corresponding to the lateral covering plates on the 
ambulacral rays. 
In the closely related Agelacrinus holbrooki (plate I, Fig, 1C), 
there was also an outer series of large ovate plates, and an inner, 
narrower series, alternating with the former, but the number of 
each was not determined. 
In Agelacrinus pileus there also is evidence of larger and smaller 
sized plates in the anal pyramid, but the outline of the pyramid 
does not appear to form as rigid a circle, and toward the center 
these plates overlap more in an imbricating manner so that the 
margins do not resemble as closely the radii of a circle. 
In Agelacrinus austini (plate VI, Figs, lA, C) the anal pyr- 
amid consists of an outer circle of 6 ovate triangular plates, 
with probably an equal number of plates forming an inner cir- 
cle, but usually hidden more or less by the outer circle. 
