1890.] Recent Literature. 161 
nopneusia) ; or they may pass beyond this Loundary, and occur upon 
the lateral walls and actinal surface (Adetopneusia). Mr. Sladen re- 
gards the former group as the more primitive, and states that the young 
of the second group pass through a stage which represents that of the 
adults of the first. 
The production of the ambulacral element in some star-fishes is 
much more rapid than general growth, thus producing a crushing to- 
gether of the plates in the direction of the length, in some cases car- 
ried to such an extent that the tube-feet in each furrow become quad- 
riserial. This last character is not looked upon as of sufficient 
importance to define the primary subdivisions of the class. The group 
in which this ambulacral crowding occurs is called Leptostroteria, 
while the group in which ambulacral development proceeds pari- 
passu with that of other parts of the body, is the Eurystroteria, and is 
by Mr. Sladen considered the older. Embryology supports this view. 
The ambital skeleton, formed of the marginal plates and their sup- 
plementaries, is looked upon as one of the most important systems of 
plates in determining form and superficial character. Here there are 
also two distinct modes of growth, that in which these plates increase 
rapidly, and continue to develop throughout the life of the star-fish 
(Phanerozonia), and that in which these plates do not increase in size, 
but, on the contrary, become relatively smaller as other parts increase 
(Cryptozonia). The Phanerozonia are regarded as the more primitive, 
especially as the young of a cryptozonate asteroid is phanerozonate. 
Two orders of the Euasteroidea are thus formed, the one, Phanero- 
zonia, combining also the stenopneusid and eurystroterid characters ; 
while the other, Cryptozonia, combines the adetopneusid and lepto- 
stroterid characters. In the first order are placed the families Archas- 
teridæ, Porcellanasteride, Astropectinide, Pentagonasteride, Anthe- 
neidz, Pentacerotide, Gymnasteriidz, and Asterinidz ; while in the 
Cryptozonia are those of Linckiidz, Zoroasteridz, Stichasteride, So- 
lasteridee, Pterasteride, Echinasteride, Heliasteride, Asteriide, and 
Brisingide. The Asterinidz, with their comparatively small marginal 
plates, approach the Linckiidz, in which the plates are large for the 
group. Mr. Sladen’s Classification is certainly the clearest that has 
been as yet formulated, and it is cheering to note that its author views 
all classification as nothing more than a working key of our views of 
affinity. 
Not less than 10g species and varieties were found at depths of from 
500 to 2500 fathoms. In most cases the actinal and abactinal 
of two to four species are given on one or more plates, and are suc- 
ceeded by magnified details of the more important external characters. 

