124 Dr. H. A. Nicholson on Species 
in the form and mode of growth of the cells, and in the posi- 
tion of the cell-mouths. It is very readily distinguished from 
the following forms by the fact that the cells are not at all 
immersed, by the fact that each cell springs directly from 
another, by the cells being strictly uniserial, and by the posi- 
tion of the cell-mouth on the front face of the swollen cell. 
The cells are distinctly pyriform in shape, attenuated below, 
with a smooth surface, the aperture being orbicular or oval 
and destitute of notches or spmes. The network formed by 
the polyzoary is usually a very close one, the branches being 
given off from the sides of the cells, usually at intervals of 
from half a line to two thirds of a line. 
All the examples of this species which I have seen are 
parasitic upon Strophomena alternata, Conrad. Hall’s speci- 
mens are from the Trenton Limestone; but there can be no 
question as to their identity with ours. 
Locality and Formation—Abundant in the Cincinnati 
Group (Hudson-River Formation) near Cincinnati, Ohio. 
2. Alecto auloporoides, Nicholson. Pl. XI. figs. 2-2 6. 
Polyzoary creeping, adnate, of narrow branches, which divide 
at various angles and repeatedly inosculate, so as to give rise 
to a complicated network, the meshes of which are more or 
less elliptical, and have a long diameter of one line more or 
less. The branches vary in width from one fifth to one third 
of a line. Cells tubular, partially immersed, free towards 
their apertures, sometimes uniserial, more commonly arranged 
in two alternating rows, sometimes irregularly disposed at the 
points of anastomosis of the branches ; from five to six cells 
in the space of one line in the narrower branches.  Cell- 
apertures terminal, circular, of the same diameter as the tube, 
the last portion of the cell being more or less conspicuously 
developed above the general surface. Surface apparently 
smooth. 
The Ohio paleontologists appear to regard this as being 
the Aulopora arachnoidea of Hall; and, indeed, it seems 
probable that Hall included this under his species. This, 
however, is an undoubted Alecto; and I think the name of 
Aulopora arachnoidea ought to be restricted to the form which 
I shall shortly describe under this name—a form which is 
very similar in general appearance to Alecto auloporoides, and 
occurs with it in the same beds, but which seems certainly to 
be an Aulopora, and is at any rate specifically distinct from 
the present fossil. 
Alecto auloporoides is very nearly allied to A. frondosa, 
