14 IOWA ACADEMY OF SCIENCES. 



Cerioniies is found in Iowa about the middle of the ISJiagara limestone, being 

 most plentiful at the horizon represented by the exposures near Maquoketa, in 

 Jackson county. The matrix is a buff or yellowish dolomite, and the fossil itself as 

 usually found, and as it was seen by Owen and Messrs. Meek ana Worthen, is a 

 more or less compressed sphere, from three-fourths of an inch to an inch and a half 

 in diameter, composed of the same material as the matrix, and marked on the sur- 

 face by shallow pits that are usually six sided, though the number of sides may vary 

 from iour to seven. The pits vary also in size, although the relations are not abso- 

 lutely constant; still in general the larger pits belong to the larger individuals. A 

 small tubular opening descends from the bottom of each pit to the center of the 

 sphere. For a good illustration of the usual appearance of the fossil the reader is 

 referred to the Geology of Illinois, volume III, plate 5, figure 2c. 



The appearance of the fossil varies with the conditions under which it was 

 preserved. There are also differences of appearance due to variations in modes of 

 growth. Meek and Worthen recognize an upper and a lower side differing in 

 respect to size and character of the pits. Whitfield speaks of a point of attach- 

 ment. From a study of a large series of individuals we may now demonstrate that 

 the normal colonies of Ceriotiites, when alive, were spherical, unattached bodies, in 

 which the structures now indicated by the pits were similar in size and other char- 

 acteristics 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 num- 

 ber and size with the pits of the surface, as we usually see it, aie very loosely 

 attached to the body of the fossil and to each other; indeed, it is evident that 

 between the individual prisms, and between the ends of the prisms and the bottoms 

 of the pits, their laminte of some sort have been dissolved out. Moreover, the 

 prijms 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 of casts. Chitinous 

 and calcareous structures are dissolved away, and the places these structures 

 occupied are, in a majority of instances, vacant; what was hollow in the original 

 fossil has been filled with the material of which the embedding rock is constituted, 

 and what was solid is simply an unoccupied space. Bearing thf se facts in mind 

 we can easilv restore the original solid parts of Cerionites. All the solid parts of 

 our present fossils of this genus from Iowa were hollow. The vacant spaces 

 between the prisms referred to. and between the wounded ends of the prisms and 

 the bottom of the shallow pits were occupied by these laminae of chitinous or cal- 

 careous matter. The small opening leading from the bottom of each pit toward the 

 center of the sphere was occupied by a slender cone that was probably hollow, 

 especially at its larger outer end. The spaces now occupied by the prisms were 

 hollow and bounded by their 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 chitinous walls, 

 80 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 stem, 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 thin chitinous or calcareous theca, that took 



