176 HISTORICAL PALZONTOLOGY. 
these and the Cystideans, is the little group of the “ Pentre- 
mites,” or Blastords (fig. 118). This group is first known to 
‘ 
Fig. 118.—A, Pentremites pyriforniis, side-view of the body (‘‘calyx”’); B, The samc 
viewed from below, showing the arrangement of the plates; C, Body of Pemtremites 
conotdeus, viewed from above. Carboniferous. 
have commenced its existence in the Upper Silurian, and it 
increased considerably in numbers in the Devonian ; but it 
was in the seas of the Carboniferous period that it attained its 
maximum, and no certain representative of the family has been 
detected in any later deposits. The ‘‘ Pentremites ” resemble 
the Crinoids in having a cup-shaped body (fig. 118, A) enclosed 
by closely-fitting calcareous plates, and supported on a short 
stem or ‘‘column,” composed of numerous calcareous pieces 
flexibly articulated together. They differ from the Crinoids, 
however, in the fact that the upper surface of the body does 
not support the crown of branched feathery ‘‘ arms,” which are 
so characteristic of the latter. On the contrary, the summit of 
the cup is closed up in the fashion of a flower-bud, whence the 
technical name of Aéastoidea applied to the group (Gr. dastos, 
a bud; edos, form). From the top of the cup radiate five broad, 
transversely-striated areas (fig. 118, C), each with a longitudi- 
nal groove down its middle; and along each side of each of 
