JUNE 28, 1912] 
echini, but represent totally different branches 
which reach their culmination in the Permian. 
(8) The Bothriocidaroid stock was the origin 
of a Cidaroid branch, which in turn gave rise 
to the Centrechinoida, and from this order all 
the other Recent echini have sprung. So 
firmly has Jackson grounded these conclusions 
on the facts of morphology, embryology and 
paleontology that it is difficult indeed to doubt 
their essential truth. Of course the time-hon- 
ored divisions Palzechinoidea and Euechi- 
noidea no longer have any use since they are 
artificial and unnatural. 
Following the key are detailed accounts of 
each of the groups given therein. Part of this 
can not avoid being elaborated repetition, but 
there is added much that is important or sug- 
gestive, particularly concerning the interrela- 
tionships of the different groups. Great im- 
portance is very naturally given to the struc- 
ture of Bothriocidaris, which is emphatically 
stated to be “the most primitive type of 
echini.” Four new genera from the Paleozoic 
are described and their relationship to pre- 
viously known forms is clearly brought out. 
The progressiveness of structure in the Pale- 
echinidse is emphasized and the ascending 
series is beautifully worked out, forming one 
of the most convincing demonstrations of 
“stages” imaginable. In this connection 
figure 237 on page 231 deserves special 
mention. 
In Part II1., “Paleozoic Echini,” is to be 
found the more distinctively systematic and 
paleontological portion of Jackson’s work, but 
it would be a great mistake for the phylogenist 
or student of variation to feel he could pass 
over this part superficially. It is crowded 
with details of morphology and of variation 
that are of very real importance. Besides 
forty species of Arch@ocidaris, most of which 
are based on fragments of spines or scattered 
plates, Jackson accepts eighty species of Pale- 
ozoic echini, grouped in 23 genera. Of these 
species, 22 are here described for the first time. 
The genera are grouped in eight families 
under four orders, but the Perischoechinoida 
with four families includes all the character- 
istic Paleozoic forms, of which satisfactory 
SCIENCE 
991 
material is known, except Bothriocidaris. 
(The Cidaroida of course are not character- 
istic of the Paleozoic and the structure of the 
Echinocystoida can not be considered satis- 
factorily known.) After a brief introductory 
note there is an interesting chapter on “ Geo- 
logical Distribution ” which will prove of par- 
ticular interest to all who have little knowl- 
edge of paleozoology. Then follow the orders, 
families, genera and species in regular se- 
quence for 208 pages. In view of its impor- 
tance in Jackson’s scheme, Bothriocidaris is 
again given particular attention. The very 
interesting fact is noted that this rare and 
extraordinary fossil was figured by Aldrovan- 
dus in 1618. Under the Cidaroida is given the 
description of a new species of Mvocidaris 
from the Lower Carboniferous of Colorado. 
The discovery of this species is of the greatest 
interest and from Jackson’s point of view of 
special importance. For the only argument 
against his phylogeny of the echini which pre- 
sented serious difficulty was the apparent non- 
existence before the Permian of echini with 
only two columns of interambulacral plates. 
While appeal might have been made with per- 
fect propriety to the “ imperfection of the geo- 
logical record,” that last resort of all hard- 
pressed phylogenists, it is far more satisfac- 
tory to have this beautifully preserved cidarid 
as tangible evidence of the existence of the 
order so far back in the Paleozoic. 
In the consideration of Paleodiscus, the ex- 
traordinary interpretation placed on its struc- 
ture by Sollas and Spencer is rejected and a 
perfectly natural explanation is offered of the 
appearance which has led to the unfortunate 
belief that the fossil represents a sort of con- 
necting link between sea-urchins and star- 
fishes. To make his record of Paleozoic forms 
complete, Jackson has included some forty 
species of Archwocidaris largely based on 
fragments but he is the first to admit (pp. 256, 
257) that most of these have little paleontolog- 
ical, less systematic and no morphological in- 
terest. Of the new genera Hyattechinus, with 
three remarkable species, two of them new, is the 
most noteworthy as it has the largest number 
of columns of interambulacral plates known 
