REVIEWS 235 
of the Icthyocrinide are arranged in a similar way to those in the 
Fistulata. Some of them have only the plate x represented, others 
only the radi-anal, still others both, and some of them have no anal 
plate at all. The Larviformia have neither the one nor the other, 
although they have frequently compound radials. The anal tube where 
it occurs, is inserted intermediate between the radials and orals. 
The systematic arrangement of the crinoids as proposed by Wachs- 
muth and Springer is one that will require but few material changes 
for a century to come. Based entirely upon morphological principles, 
with a completeness and wealth of ontogenetic and phylogenetic data 
that is rarely obtainable among fossil organisms, the essential elements 
of classification are more firmly grounded than perhaps in any other 
group. No attempt in recent years towards a natural and rational orderly 
arrangement of a large and complex assemblage of organic remains has 
been so signally successful. Nor has the evolution of the groups in 
time and space been neglected. For classificatory purposes special 
emphasis should be placed upon a number of features. Of very great 
importance is the growth of the stem, whether the young joints are 
formed beneath the proximal ring of the calyx or beneath the top 
stem joint. Particular stress is also to be placed on the alternate 
arrangement of the stem with the lower ring of plates in the calyx, by 
which it is determined that by far the large majority of the neozoic 
crinoids are dicyclic and not monocyclic. Of exceptional significance 
are certain features in the Ichthyocrinide which clearly indicate affini- 
ties with the Apiocrinide, Bourgueticrinide, Eugeniacrinide, and 
Comatule all five groups of which are placed together among the 
Articulata. All have a disk composed of small, irregular, and movable 
pieces, with open mouth and open food grooves, all are dicyclic, but 
the infrabasals coalesce with the top stem joint, so as to prevent the 
introduction of new joints directly beneath the calyx. From the Artic- 
ulata are excluded the Encrinide and Pentacrinide which are gener- 
ally arranged with them. The infrabasals of the former of the two 
families are very small, or are resorbed in the growing animal, but 
they do not coalesce with the top joint which is therefore for the 
time being the youngest joint of the stem. The Pentacrinide have, 
through the Encrinide, close affinities with the Poterocrinidz, and prob- 
ably are their descendants, but if they really belong to the Inadunata as 
is now believed they represent somewhat abberant types, for the lower 
brachials take part in the calyx. 
