BEATRICEA-LIKE ORGANISM FROM THE MIDDLE ORDOVICIAN. 
9 
and one such has the clear band 2 • 5 mm. wide. The presence 
of this structureless “clear zone” explains the state of preser- 
vation of most of the specimens found on the weathered sur- 
faces of the rocks. It being either hollow or filled with a soft 
substance, the outer sheath zone and the axial tube were easily- 
separated, and in the specimens usually found such separation 
had occurred before the specimens were buried in the rocks. 
Summary. Transverse sections of Crytophragmus anti- 
quatus show that it is composed of three distinctly separated 
and well marked concentric layers. The inner axial tube has 
a large cavity, divided into chambers by bulging partitions, and 
around this cavity is a narrow band of cystose tissue, without 
radial elements of any kind. The axial tube has a well-defined 
outer wall, and is surrounded by the second zone which seems 
to be structureless and is usually marked by a band of clear 
calcite. The outer zone is composed of concentric sheaths 
traversed by numerous radial canals. 
Comparison with Beatricea nodulosa and B. undualata . 
The skeleton of this species has a much smaller habit than 
either of Billing’s species and the surface is evidently much more 
nearly smooth. As to the internal structure, as revealed by thin 
transverse sections, there seem to be rather striking differences. 
A distinct differentiation into three zones exactly comparable 
to those described above has not been noted by students of the 
above species. As noted above, the sections given by Nicholson 
in figures 2 and 3 of Plate VIII of his article do not appear to rep- 
resent a section of a complete skeleton, as Nicholson supposed, 
but are comparable to the axial tube of Cryptophragmus anti - 
quatus . If this latter comparison is correct, then the central 
tabulate zone of B. nodulosa is very small as compared with that 
in the axial tube of B. antiquata r and the surrounding cystose 
zone very thick. In C. antiquatus there are no indications 
of radial elements in the cystose zone, nor are there anywhere 
the granular deposits on the walls, such as both Nicholson and 
Parks have described. As seen in this section the walls are 
perfectly sharp, and though each wall has a cloudy border, this 
border, as seen under a high power, seems to be due to alter- 
