Cerionites Dactylioides Owen. — Calvin. 55 
in which Owen probably intended to write it, or dactylioides, 
the more correct spelling employed by Meek and Worthen. 
Cerionites is found in Iowa about the middle of the Niagara 
limestone, being most plentiful at the horizon represented by 
the exposures near Maquoketa, in Jackson county. The ma- 
trix is a buff or yellowish dolomite, and the fossil itself as 
usually found, and as it was seen by Owen and Messrs. Meek 
and Worthen, is a more or less compressed sphere, from three- 
fourths of an inch to an inch and a half in diameter, com- 
posed of the same material as the matrix, and marked on the 
surface by shallow pits that are usually six sided, though the 
number of sides may vary from four to seven. The pits vary 
also in size ; although the relations are not absolutely con- 
stant, still in general the larger pits belong to the larger in- 
dividuals. A small tubular opening descends from the bot- 
tom of each pit to the center of the sphere. For a good illus- 
tration of the usual appearance of the fossil the reader is re- 
ferred to the Geology of Illinois, volume iii, plate 5, figure 2c. 
The appearance of the fossil varies with the conditions un- 
der which it was preserved. There are also differences of ap- 
pearance due to variations in modes of growth. Meek and 
Worthen recognize an upper and a lower side differing in re- 
spect to size and character of the pits. Whitfield speaks of a 
point of attachment. From a stud} r of a large series of in- 
dividuals we may now demonstrate that the normal colonies 
of Cerionites, when alive, were spherical, unattached bodies. 
in which the structures now indicated by the pits were simi- 
lar in size and other characteristics over the entire surface. 
On the surface of a number of our specimens we have a series 
of prisms, about a tenth of an inch in length, with their 
inner rounded ends resting in the concave pits. These prisms, 
which correspond in number and size with the pits of the 
surface, as we usually see it, are very loosely attached to the 
body of the fossil and to each other; indeed, it i> evident that 
between the individual prisms, and between the ends of the 
prisms and the bottoms of the pits, thin lamina' of some sorl 
have been dissolved out. Moreover, the prisms are of the 
same material as the matrix, and also of the same material as 
the fossil itself. 
Now. in all our dolomites the fossils are usually in the form 
