624 The American Naturalist. [July. 
specimens. This species is known to occur only in the Rockford 
shales at Owens' Grove, Hackberry and Rockford, Iowa.« Although 
this species is not uncommon at the former locality, yet less than a 
dozen specimens have been secured from the two latter places during 
the thirteen successive years that we have collected from these shales. 
This is a fine species, and cannot well be confounded with any other 
described in this country. 
Pachyphyllum ordinatum n. sp. — Coral compound, growing in regular 
convex, hemispherical masses, ten centimetres in diameter; point of 
attachment small. Cell walls abruptly but usually slightly exsert ; 
generally projecting only one and one-half mm. above the intervening 
spaces ; central depressions circular, very regular, three mm. in diame- 
ter (rarely a few small young cells are present); entire cells, quite 
uniform in size and of moderate dimensions, partially limited by a 
wall formed by the uniting of the costae from the adjoining cells. 
Number of rays, from twenty-seven to thirty-two, most of which extend 
to the slightly elevated centre. Rays and costae continuous, passing 
down the outside of the cell wall and over the intercellular spaces. 
Rays and costae in well-preserved specimens, slender ; but in weathered 
specimens, strong and broadly rounded or angular. The surface of 
each cell of this species is slightly concave ; sometimes the exsert por- 
tion of the cell (which always occupies the centre of the entire cell) 
is sunk below the outer wall of the cell. This species varies much 
from P. woodmani in its general aspect, the concave surface and greater 
regularity of the cells, as well as in several other important particulars. 
Position and locality : Rockford shales, Hackberry, Iowa. 
Pachyphyllum crassum n. sp. — Coral usually growing in concave or 
convex hemispherical masses, from two centimetres to eight centime- 
tres in diameter. Cells usually large, walls strongly exsert, often 
projecting four mm. above the intervening spaces ; central depressions 
quite regular, from three to five mm. in depth ; entire cell from two 
centimetres in length to one and one-third centimetres in width ; when 
this size is attained, however, it is at the expense of the adjoining cells. 
At times the large exsert portions of the cells are so crowded together 
