98 TIREE CRUISES OF THE / BLAKE." 
during the cretaceous and jurassic periods. They are, with the 
Pourtalesiz, the forerunners of the true spatangoids. They have 
many features in common with the flat clypeastroids, such as 
their tuberculation, the character of their pedicellarie and 
spines, and the structure of the apical system (Fig. 366), while 
the structure of the anal system and the general facies of the 
test rather allies them to the true spatan- 
goids. But neither the Nucleolidee nor the 
Pourtalesie are possessed of fascioles, an 
eminently spatangoid structure. These 
specialized bands of minute spines are 
slightly developed in some of the creta- 
ceous genera, and their rudimentary form 
exists to-day in such types as Hemiaster. 
Their exact function is not yet known. 
They take their greatest developments in 
such modern genera as Schizaster. Some 
light has been thrown on their development by the discovery 
of a deep-sea species of Macropneustes, which shows a gradual 
transition between the tuberculation of the test (Fig. 367) and 
specialized areas corresponding to fascioles. 
Fig. 366. — Neolampas 
rostellata, magnifieg. 
Fig. 367. — Macropneustes spatangoides. +. 
important bearing as indieating the spe- characteristic of the West Indies since 
cies which are likely hereafter to be pre- the earliest tertiary. We cannot expect 
served as fossils, and shows us how diffi- to find represented among the fossils the 
cult it may become, even when we have Eehinothurise, Pourtalesise, and many of 
such an abundant and characteristie echi- the Echinid:e, since after death they read- 
nid fauna as that of the West Indies, to ily fall to pieces, and may then be dis- 
reconstruet it from the future fossils. solved, like many species of mollusks, at 
We may also notice that the genera of great depth, before they become protected 
which we so frequently find the dead tests bya covering of deep-sea ooze. 
are the same which have been known as 
