380 Agassiz— Paleontological and Embryological Development. 
ticha ; a greater number of coronal plates, the development of 
secondaries and miliaries combined with a specialization of the 
actinal system not found in the Cidaride. : 
An examination of the succession of the Echinoconide shows 
but little modification from the earliest types; the changes, 
however, are similar to those undergone by the Clypeastroids 
and Petalosticha, though they do not extend to modifications 
of the poriferous zone, but are mainly changes in the actinos- 
tome and in the tuberculation. In fact, the-group of Echino- 
sistency of the types preceding the Kchinoneidw and the 
Ananchytide, which have remained without important modifi- 
ree with the changes which have been observed in the 
growth of Echinolampas. The early genera, like Pygurus, 
have many of the characteristics of the test of the young Echi- 
nolampas. The development of prominent bourrelets and of 
the floscelle and petals goes on side by side with that of genera 
in which the modification of the actinostome, of the test, and 
of the petals is far less rapid, one group retaining the Echino- 
neus features, the other culminating in the Echinolampas o 
the present day, and having likewise a persistent type, Echino- 
rissus, which has remained with its main structural features 
unchanged from the Jura to the present day. That is, we find 
genera of the Cassidulidee which recall the early Echinoneus 
stage of Echinolampas, next the Caratomus stage, after which 
the floscelle, bourrelets, and petals of the group become more 
prominent features of the succeeding genera. Accompanying 
the persistent type Echinobrissus, genera appear in which either 
the bourrelets or petals have undergone modifications more 
extensive than those of the same parts in the genera of the 
Kchinoneus or Caratomus type. 
The earliest Spatangoids belong to the Dysasterids, appa- 
rently an aberrant group, but which, from the history of the 
