56 Tin American Geologist. July, 1893 
of casts. Chitinous and calcareous structures are dissolved 
away, and the places these structures occupied ;tn\ In a ma- 
jority of instances, vacanl ; whal was hollow in the original 
fossil has been filled with the material of which the embed- 
ding rock is constituted, and what was solid Is simply an un- 
occupied space. Bearing these Tacts in mind we can easily 
restore the original solid parts of Cerionites. All the solid 
parts of our present fossils of this genus from Iowa were hol- 
low. The vacant spaces between the prisms referred to. and 
between the rounded ends of the prisms and the bottom of 
the shallow pits were occupied by thin lamina? of chitinous or 
calcareous matter. The small opening leading from the bot- 
to f each pit toward the center of the sphere was occupied 
by a slender cone that was probably hollow, especially at it- 
larger outer end. The spaces now occupied by the prisms 
were hollow and hounded by thin walls, constituting the 
laminae already mentioned; so that we would get, as a result 
of our efforts to restore the solid parts of the original organism, 
a number of shallow, polygonal coherent cups, with thin chiti- 
nous walls, so arranged as to enclose a spherical space, each cup 
sending toward the center of the sphere a slender radial tube 
or rod of the same chitinous material. The tubes or rods were 
certainly very delicate at the center of the sphere, at which 
point they were probably all more or less intimately united 
and from which they diverged as radii, one to the bottom of 
each cup. 
Cerionites, therefore, was a colony of individualized units 
of some sort. Each separate individual was surrounded by 
a thin chitinous or calcareous theca that took the form of a 
shallow polygonal calyx. Each was united to the center of 
the sphere, the point at which growth began, and from which 
it proceeded outward along radial lines, by a slender thread of 
protoplasm which was also inclosed in a delicate chitinous 
-heath. The colony was free and doubtless moved through 
the water with the graceful rolling motion that characterized 
colonies of JJvella and Synura. The movements of the still 
more beautiful and much more familiar Volvox globator will 
convey to users of the microscope a correct idea of a mode of 
locomotion 1 fancy they might have witnessed, without the 
aid of the "tube," in all the sheltered coves of the Upper Si- 
