256 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Surface of plates smooth or finely granulose; the radial plates somewhat 
elevated along their median lines; sutures distinct, but not grooved. 
Infrabasals larger than in any other known species of this genus, and 
plainly visible from a side view, forming a shallow cup. Basals large, a little 
higher than wide, upper face narrowly truncated. Radials and costals of 
similar size; the former pentagonal, the two costals hexagonal, except in 
the posterior rays in‘ which the second is heptagonal. Distichals to the 
height of the sixth plate incorporated into the calyx, gradually decreasing 
in height; the first as large as the second interbrachials, the upper one 
resembling a good sized arm plate. Arms short, delicate, twice bifureat- 
ing; composed from their bases up of small triangular interlocking pieces. 
Interbrachials: 1, 2, 2, 2, ete., rarely 1, 2, 3, 3, the lower plate heptagonal, 
larger than the radials; at the anal side there are three plates in the second 
and all succeeding rows. Interdistichals nine or more, rather large. Struc- 
ture of ventral disk and anus not known. Column circular, slightly tapering ; 
in the upper part of the stem the nodal joints project, but further down have 
the same size as the others. 
Horizon and Locality.— Trenton limestone ; Montreal, Canada. 
Types in the Canada Survey Museum at Ottawa. 
Archeocrinus microbasalis Brivxrves. 
Plate X. Figs. 2a, b, ¢. 
1857. Thysanocrinus (Rhodocrinus) microbasalis —E. Bruurncs; Geol. Rep. Canada (Rep. of Progr.) 
p. 264; also ibid., Decade IV., p. 63, Plate 6, Fig. 2. 
1881. Archeocrinus microbasalis —W. and Sv.; Revision Paleocr., Part IT., p. 190. 
Smaller than the preceding species, the arms proportionally longer. 
Calyx obconical, truncated at the lower end, sides slightly convex. Surface 
beautifully ornamented with parallel, radiating striae, proceeding from the 
middle of the plates to adjoining ones, and broad, rounded ridges, starting 
from the middle of the radials and passing up the costals and distichals into 
the free arms. 
Infrabasals minute, forming a pentagon, which rests within the basal con- 
cavity and is covered by the column. Basals large, heptagonal, more than 
two thirds of the plates visible from a side view, the lower end bent inward 
and forming, together with the infrabasals, a good sized concavity, with a 
thickened rim around the edge; the upper faces narrowly truncated, Radials 
as large as the basals, distinctly angular below; the costals somewhat smaller, 
