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ACROCRINID &. 809 
The basals are followed by from fifteen to twenty rings of accessory pieces — 
the number varying among the specimens — and each ring consists of twenty 
to twenty-four plates, except the two upper rings, which contain but twelve. 
Of the upper ring, seven plates are arranged interradially — three occupy 
the anal side and one the regular sides — which alternate with the radial 
pieces, Most of the accessory pieces are hexagonal, and angular at top 
and bottom; but at the anterior and posterior sides those constituting the 
middle series are truncated at both ends. Radials large, one third wider 
than long, deeply excavated at the upper face into a facet which contains 
the costal and both distichals. Anal plate of the same width as the radials 
but considerably longer. It supports several small plates, which project 
outward, and may be readily taken for the base of an arm. Costals wider 
than in the two preceding species, but equally short; the distichals propor- 
tionally longer and narrower, rounded on the back, and distinctly curving 
outward. Palmars free from the second or third plate, curving outward and 
downward, bringing the arms into a pendent position, their backs next to the 
calyx, and the ambulacra and pinnules on the outside. Arms twenty, moder- 
ately long, descending far beyond the basals; they are composed from the 
fourth or fifth plate of two series of rather short joints, and rest, apparently 
immovably, with their backs within deep longitudinal grooves or impressions 
on the surface of the dorsal cup. Pinnules long, closely packed; composed 
of long joints three times as long as wide, their ventral furrows, like those 
of the arms, lined by two rows of covering pieces. Ventral disk flat, 
the middle portions composed of numerous small perisomic plates, from 
which well defined ambulacral pieces, alternately arranged and suturally 
united, curve downward, and pass out into the arms. Anus eccentric, on 
a level with the upper surface, placed about half way between the centre of 
the disk and its outer margin. Column round, the joints nearly of equal 
size. 
Horizon and Locality. — St. Louis group; near Huntsville, Ala., where 
we obtained a considerable number of specimens. 
Types in the collection of Wachsmuth and Springer. 
Remarks. — This species is readily distinguished from A. Shwmnardi by 
its smaller size and recumbent arms, and from A. Wortheni by the different 
form of the calyx and the much smaller number of accessory pieces of that 
species. 
The arms of this species were apparently immovable, as is indicated by 
102 
