50 
larity of the column nearthe pelvis, we may readilyadimit a continuing new form- 
ation of joints, by the muscular integuments developing and: increasing in size. 
Avxiviary Sipe Arms. (Pu. 1) In the late Mr. Tosin’s specimen, 
near the fractured! end, at intervals of every 15th, 14th, or 12th jeint, auxiliary 
side arms proceed from each of the five spaces intervening between the petal- 
like divisions; further up they come off from every Sth, 6th, and 4th, and near 
the pelvis from every second joint. The intervening space between the petal- 
like divisions being only near the centre calcareous, is peculiarly adapted to 
supply the auxiliary side arms with nourishment, and to afford them points 
of attachment, they have here also a more convenient space for action and 
motion. Each of the columnar joints from which they proceed has five oval, 
transverse, and slightly concave impressions, surrounded by a rim sometimes 
having a few radiating stri, Across the greatest diameter of the ellipticareais a 
ridge, having in its centrea perforation admitting the nourishing vessel, probably 
supplied by vessels proceeding from the alimentary canal. Each auxiliary arm 
(PL. u. fig. 22.) when full grown is formed by about forty joints, of which those 
near the column are more or less oval and thinner, the following becoming 
thicker and rounder, but decreasing in size, their surface slants with an angle 
of about twenty degrees from the perpendicular line of the column, admitting a 
free motion upwards (on which side they also show a kind of fold) but op- 
posing a movement downwards. The articulating surfaces (Px. 11. fig. 15. to 
17.) are surrounded by an elevated rim, the interior is excavated into two cir- 
cular concavities of unequal size, so disposed as to resemble the figure 8. the 
two circles forming it, being separated by a small transverse ridge perforated by 
the central passage of the nourishing vessel. (Pu. 11. fig, 23.) The termination 
of the auxiliary side arms is a conic hooked joint, of a polished, greenish, en- 
ameled appearance; whereas the rest of the animal is of a pale yellow colour. 
Near the summit of the column, about the fourth series of auxiliary side arms 
from the pelvis, they become shorter and thinner; here evidently showing 
their greater muscularity, bend very slightly, and have their joints, particularly 
those near the point (which as yet is not hooked) but faintly developed. (Pu. 
11. fig. 21.) Those of the second series from the summit, are short, round, spine- 
shaped, and particularly near the point so muscular, that not even the termi- 
nating joint is discernible. (Pu. 2. fig. 20.) The first series of auxiliary side 
arms (inserted ona joint which the lower protruding part of the first costals 
almost touch) is still shorter, and almost resembles in appearance and thick- 
ness a bristle. ‘The formation of the lower side arms demonstrates the growth 
