PALEONTOLOGY OF IOWA. 477 



elevation which rises as high as the outer walls. In the un- 

 worn cells the inner wall rarely presents any interruption to 

 the rays, some of them dying out or becoming less distinctly 

 denticulate within this area. 



The specimen figured is much weathered, and its outer area exhibits a gently in- 

 clining surface and a deep depression within the inner wall, with a scarcely elevated 

 point in the centre. Other specimens, with the cup entire, are less depressed; and 

 some specimens, which do not appear to have been worn before imbedding, are 

 scarcely depressed within the inner walls. 



Although these differ in some slight degree from the figures and descriptions cited 

 above, I am inclined to regard them as identical, more particularly since specimens 

 from different localities in Iowa show a considerable variation in external appearance 

 as well as in the prevailing number of rays. The cells range in their greatest dia- 

 meter from one-quarter to one-half an inch, presenting upon the surface of large 

 specimens every degree of development. 



Fig. 8 a. A weathered fragment of this species. 

 Fig. 8 b. An enlargement of one of the cells. 



Geological formation and locality. In limestone of the age of the Ha- 

 milton group of New- York : Near Davenport, Rockingham, New-Buffalo, 

 Pine creek, Iowa city and other places in Iowa ; Hamburgh, etc. in Illinois. 



Aceinilaria profunda (n. s.). 



PLATE I. FIG. 7 a, b, c. 



CORAL astrseiform, subhemispheric ; cells irregularly poly- 

 gonal, unequal in size, often somewhat circular in the young 

 and half grown conditions ; walls thin, scarcely undulating ; 

 inner wall undefined ; cup abruptly and deeply depressed 

 from a little within the outer wall ; centre marked by a pa- 

 pilliform node : rays thin, slender, from 36 to 46 in each 

 cell (41 to 46 in full grown individuals), denticulate on the 

 sides from the margin to the base of the cup ; some of the 

 rays disappearing between the margin and the centre. 



This species, in general aspect and in details of structure, is very distinct from 

 A. davidsoni. The cells are less compactly arranged, and the outline is often some- 

 what circular, particularly in the young state. The cells are very unequal in dimen- 

 sions, even in the same specimen, and this difference in the size is not always 

 accompanied by a corresponding difference in the number of rays. The walls of this 

 species are less strong than those of the preceding species, and scarcely undulating; 

 while the rays are much more slender, and the denticulations more regular. 



