THE TRENTON CRINOID, OTTAWACRINTJS 
7 
The fragments of the remainder of the stem show that it con- 
tinued to taper until it reached a mean diameter of about 2 * 2 
mm. This was probably at a distance of about 15 mm. from the 
cup. After that, the stem gradually increased in diameter, 
until at a few millimetres above the root the mean diameter is 
4-3 mm., and 4* 1 mm. immediately above the branching of the 
root. 
Near the root the stem is slightly quinquelobate, the lobes 
corresponding with the pentameres. The section at the broken 
end of the fragment attached to the cup is neither circular nor 
sub-circular, but clearly subpentagonal, the convexities corres- 
ponding with the pentameres (Plate I, fig. 8.) 
Just above the root the average height of a pentamere is 0-45 
mm. In a region where the mean diameter is 3 • 35, the average 
height of a pentamere is 0 * 58. In this region, however, the pen- 
tameres alternate in thickness. 
Even in the distal region the pentameres of one vertical section 
do not alternate or interlock quite evenly with those of the ad- 
jacent sections, but one of the end-slopes of each pentamere is 
shorter than the other. In the region where the pentameres 
alternate in thickness, the relations of the sections are still less 
regular, for a thick pentamere may abut at one or both of its 
ends on one thin and two thick pentameres of the adjacent sec- 
tion, so that its outline is 7- or 8-sided instead of 6-sided. This 
is shown in the enlarged figure of a suture by Billings (1887) and 
in our fig. 9 (Plate I). Thus the centres of adjacent pentameres 
come to lie at the same level, and the transition to regularly 
abutting pentameres of equal size is easy. 
In the distal region the upper and lower joint-faces of the 
pentameres are marked with striae formed of concresced granules 
(Plate I, fig. 7). The striae radiate towards the periphery, 
branching slightly as they go. The same arrangement is visible 
in the middle region. Nearer the cup the strise become coarser 
and change into distinct ridges (Plate I, fig. 6). These ridges 
then shorten at their adeentral ends, especially near the middle 
line of each pentamere, so that there is left a smooth or faintly 
granular area of rather indistinct petaloid shape. This area 
increases at the expense of the ridges as the cup is approached, 
and on the under joint-face of each pentamere it seems occa- 
