Geology and Mineralogy. 1155 
echinoderms as constituting a class, for which they adopt Leuck- 
art’s appropriate name, Pelmatozoa, thus distinguishing them 
from Ophiurans, star-fishes and sea-urchins, which are character- 
ized by locomotion and the downward position of the mouth. 
The Pelmatozoa are divided into two well-marked sub-classes, 
namely, the Crinoidea of Miller, embracing all brachiate crinoids, 
with the orders Neocrinoidea and Palzocrinoidea; and the 
Anthodiata, or armless forms, including the orders Blastoidea 
and Cystidea. . 
Three sub-orders are proposed, to include all the known forms 
of the Paleocrinoidea. (1) The Camarata, which are the typical 
Palzocrinoids, having the plates. of the test solidly united by 
suture and having the lower armplates incorporated into the 
calyx by means of interradial plates. Actinocrinus is a typical 
form of this sub-order. (2) The Articulata, which are character- 
ized by an articulate structure of the calcareous skeleton, which 
renders it more or less pliable, as in Ichthyocrinus. (3) The 
Inadunata, which have the arms free from the first radials up- 
ward, as in Cyathocrinus. These three groups are found to be 
also respectively characterized by differences in the construction 
of the summit, which the authors consider to be subordinate to 
and consequent upon the fundamental modifications in the plan 
of structure above mentioned. 
_ The authors subdivide the Inadunata into two groups, namely, 
the Larviformia and the Fistulata. The former group includes 
such embryonic, or permanent larval, forms as Haplocrinus and 
Symbathocrinus. The latter group embraces forms which have 
the ventral portions of the body expanded or elevated into a 
porous ventral sac, of variable size, of which Cceliocrinus pre- 
sents an extreme example. 
The several groups are separated into many families, some of 
which are sharply defined, while others shade into each other by 
perplexing transitional forms. The generic relations of the 
Palzocrinoidea are minutely discussed, and a detailed diagnosis 
of each genus is given, which is followed by a list of all the 
species which the authors consider to be properly referable to 
the genus. The synonymy and references to the literature of 
each species is also given in full, At the end of the work is a 
complete catalogue of species, which serves both for an index 
and a synonymic list. This very valuable feature of works of 
this kind is too often entirely neglected by authors. 
The morphological discussions in Part III deal with interesting 
questions in relation to homologies between different parts of the 
widely divergent types of recent and fossil crinoids.. In the 
early larva of the living crinoids the abactinal sice, so far as at 
present -known, consists of only five basals, forming a cup. The 
actinal side consists of a closed pyramid of five plates; the 
latter covering the mouth. Subsequently the radials, and after- 
ward the arms, appear. The appearance of the basals and orals 
at the same time, the one occupying the oral and the other the 
