(36 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
Gallery 
VIII. 
Table-case 
30. 
former are among the Bohemian and French Cystids, the 
last is well .shown among the British fossils. 
Class BLASTOIDEA. 
Drachioles 
Deltoids - 
Itadials - 
JlasaU ■ ■ 
Theca 
The Blastoids (Bud-shaped) form a small class of Echino- 
derma, which arose at an early period, probably from Cy.stidea 
l)iplo])orita, and flour- 
ished chiefly in Devo- 
nian and Carboni- 
ferous times. The 
Museum possesses a 
rich collection, which 
served as basis of a 
monograph written by 
Etheridge and Carpen- 
ter and published by 
the Trustees. A list 
of the specimens has 
also been issued. 
Since the fossils are 
too small to be seen 
clearly, only a few 
characteristic, exam- 
ples are exhibited. 
The general appear- 
ance of the blastoid 
skeleton and the term.s 
applied to its more 
obvious parts are 
shown in Fig. 30. The 
brachioles border five 
food-grooves, of which 
the skeleton is rather 
complicated. The con- 
tiguous edges of the 
plates termed deltoids 
and radials were 
folded, and in most of 
the genera these folds 
projected far into the 
interior of the theca 
and thus enabled the 
Fig. 30.— a typical Blastoid, Oroplwcrinus fusi- ^grated sea-water to 
fannis, Carboniferous (Kinderhook) of Iowa, 
XJ«S«A« 
Hoot 
