52 BRITISH PALAZOZOIC FOSSILS. [ Ecu1nopERMATa. 
of the madreporiform tubercle of the Starfishes defined their posterior interambulacral space, and the oppo- 
site ray, like the opposite ambulacrum of the Echinidan, becomes the anterior one. 
Divided into the orders:—1, Crinoidea ; 2, Blastoidea; 3, Ophiure ; 4, Asteriw; 5, Perischoechinide ; 
6, Echinide ; 7, Holothurie ; 8, Sipunculide ; 9, Cystidea. The 7th and 8th being naked and soft, are not 
known in the fossil state, the former in other respects resemble the Hchinidw, the latter so far resemble worms 
externally as to be so classed by Agassiz. 
Ist Ord. CRINOIDEA. 
Viscera enclosed in a cup of numerous polygonal, calcareous plates; mouth surrounded by five solid, 
prehensile, branching rays, set on the inner side with jointed fimbriated tentacles ; attached to foreign bodies 
either permanently or in the young state, from the middle of the back by a long flexible jointed column, 
perforated by an alimentary canal, and often furnished on the sides with slender pointed “auxiliary side- 
arms” of numerous joints, to aid occasionally in securely anchoring the stem. 
To avoid the discrepancies which exist between the opinions of Miller, Phillips, Austin, &c., as to which 
plates of the cup should in all cases bear the distinctive terms, Pe/vis, 1st and 2nd costals, &c., proposed 
by Miller, and used even by himself in a different sense in different genera, I would propose the following 
system of nomenclature for the plates, which is applicable to the most complex as well as to the most simple 
cups, and will enable us to particularize any individual plate for description (which cannot be done accord- 
ing to the methods employed by MM. Agassiz and D’Orbigny, who define their genera simply by enumerating 
the number of rows of plates forming the cup, and without giving any greater importance to the normal regular 
lines, than to the irregular intercalated ones). In reviewing the whole class Hehinodermata, we must be struck 
with one of the most persistent characters of the group, namely, the disposition of the organs of prehension 
or locomotion in five rays round the mouth—this is without exception in the higher groups, as the Hchinide ; 
in the lower Asteriw they are occasionally more numerous; in the lower Ophiure they again resume the 
typical number, and the prehensile arms of the Crinoids, are with very few exceptions, five in number at their 
origin. Taking this as a starting point, we may call the co/wmn and its appendages, and the first row of 
plates resting immediately on it, forming the pelvis, by the old names of Miller. The five plates usually 
found resting on the pelvis, I propose to call lst primary radial plates, as they are the first of the vertical 
rows which form, or originate, the rays; on the upper edge of each of these rests the 2nd, and vertically 
over that, the 3rd, &c., primary radial plates, as far as the first cuneiform or pointed joint, the number 
varying with the genus without, on this system, occasioning any ambiguities, each individual plate of the series 
being only distinguished by a numeral. The last or cuneiform joint, originates a double set of plates, or 
branches, and these I propose calling the secondary radials as far as their last or cuneiform joint, distin- 
guishing each individual, as before, by a numeral, commencing from the base. The succeeding branches 
are unimportant, never forming part of the cup, and do not require particular names. When (as in Acti- 
nocrinus) six joints rest on the pelvis, only five of them originate vertical rows going to the rays, and I 
propose to call the intercalated plate Ist interradial ; the two plates resting on its pointed summit I would call 
2nd interradials, as well as the plates at the same level in the other four spaces between the primary radial 
rows; the plates resting on the 2nd interradials I would call 8rd interradials, and so on without limit. 
The rows of interradial plates alternate with those below and above them, and never form vertical con- 
tinuous lines like the radials. To give an example of the superior precision and simplicity of this notation, 
we may take two well-known genera—Platycrinus and Actinocrinus: the first has a very simple cup of one 
row of plates, the other has a very complex cup of numerous rows. In Platycrinus the five plates resting 
on the pelvis are named scapule by Miller and most succeeding writers, and the five rows resting vertically 
on them as far as the first cuneiform joint, he terms arms; the two rows of plates going from each first 
cuneiform joint, he calls hands. In Actinocrinus, however, he calls the six plates, resting on the pelvis, 
Ast costals, although one of them is abnormal, and the other five are precisely the same plates which in Pla- 
tycrinus he called scapule ; the next row he calls 2nd costals, although identical with those called arm-joints ; 
