to Micro-Paleontoloqy. 125 
lar, ordinary examples having a height of an inch or an inch 
and a half, anda diameter of about the same at the base. The 
base is flat or concave, and is covered by a striated epitheca ; 
and the corallites radiate from the base to open over the whole 
convex upper surface of the colony. The corallites are pris- 
matic, mostly pentagonal, thin-walled, and not firmly united 
with one another, their walls being regularly and uniformly 
crenulated in such a manner that contiguous tubes are accu- 
rately dovetailed together. The corallites vary in size from 
about -'5 inch up to 3; inch, there being occasionally definitely 
defined groups of the larger tubes. No spiniform tubuli are 
developed. ‘The surface is apparently smooth and devoid of 
Fig. 2. 
c 
Monotrypa crenulata, Nich. A, outline of a specimen, of the natural 
size; B, part of a few tubes, enlarged; C, longitudinal section, enlarged 
twenty times; D, tangential section, similarly enlarged. 
monticules. As seen in long sections the tubes are found to be 
crossed at considerable intervals (s'5 to 75 inch) by a few 
horizontal tabule, which are not uniformly placed at corre- 
sponding levels in contiguous corallites. 
