ECHINONEUS CYCLOSTOMUS. 61 
it was shed, or liberated spontaneously. A resorption similar to that which 
occurs in some parts of the test, appears more probable. In what manner the 
oesophagus follows this change, and from a tiny tube inserted at the centre of 
the pyramids, becomes funnel-shaped at its lower end and fastened to, or near 
the pentagonal nerve and water-vascular canal, which remains permanent 
on the buccal membrane, is a matter of conjecture. 
The auricles are disconnected, minute and flattened to the ambulacral 
plate (Pl. 11, figs. 5, 6). The largest part of their surface is covered by a mus- 
cular attachment. Their resorption is probably contemporary with the dental 
parts. 
The pyramids (PI. 12, figs. 4-8), have deep foramina, a little over one third 
of the height, are slightly concave on the inside, and somewhat keeled on the 
outside parallel to the tooth. The adjacent edges are thin, and the corrugations 
absent. The outline, narrow at the summit, and the lower tapering end, differ 
considerably from the figure of Discoidea, given by Hawkins (Geol. Mag., 
new ser. Decade V. April, 1909, 6, p. 148-152, pl.6). The compass (Pl. 12, 
figs. 11, a. b), is distinctly articulated, and when seen in profile curves at the 
outer end. 
The scapula-shaped epiphyses without being united to the pyramid (PI. 12, 
figs. 1, 12 a. b), follow the brace horizontally, and are held in place by connecting 
tissue; this could have been seen (PI. 1, fig. 7), if its minuteness had not pre- 
vented removal of the membrane, which would have displaced the parts. The 
braces do not show any special peculiarity in form. 
Seen in profile the strong tooth (PI. 12, figs. 9 a. b. ¢), is distinetly curved 
with a high keel on the inner face and a shallow groove on the outer. 
THe ALIMENTARY CANAL. 
Plates 8-10, Plate 11, figs. 8, 9. 
Although the Jamaican specimens were in very good condition for examina- 
tion, having been in alcohol only a few days, still several important points of 
anatomical detail remain for future study on living specimens, and the figures 
given are limited to the alimentary canal, and the associated reproductive organs. 
The oesophagus rises vertically from the buccal membrane in a thin transparent 
funnel-shaped tissue, which tapers quickly into a tiny tube (PI. 10, fig. 5), and 
extends nearly half the height of the test, where close to the insertion of the 
actinal intestinal appendage it enters the actinal loops of the alimentary canal 
