of Alecto and Aulopora. 127 
Some examples of this species are branched with tolerable 
regularity, as in the specimen figured ; but others form com- 
pressed and closely interlaced reticulations. No positive or 
absolutely definite characters can be stated which would lead 
to the reterence of this fossil to Awlopore rather than to Alecto. 
Nevertheless the general aspect of the fossil is such that it 
can almost positively be placed under the former genus. The 
forms to which it presents the nearest alliance are A. filiformis, 
Billings, and A. (?) canadensis, Nich., both of which are De- 
vonian ; but it is readily distinguished from these, and by no 
character more conspicuously than by the fact that the corallites 
open in the axis of the branches, instead of making an angle 
with the main stems. With a little care, also, there is no 
great difficulty in separating it from Alecto auloporoides, to 
which it presents a very considerable superficial resemblance. 
The examples of Awlopora arachnoidea described by Hall 
are from the Trenton Limestone; but ours are from a higher 
horizon. The specimens which I have seen are all attached 
parasitically to the surface of different species of Chetetes 
(Monticulipora). 
Locality and Formation—Cincinnati Group, Cincinnati 
and Waynesville, Ohio. 
EXPLANATION OF PLATE XI. 
Fig. 1. Hippothoa inflata, Hall, sp., a small fragment, greatly enlarged. 
1a. Two of the cells of the same, still further enlarged. 
Fig. 2. Alecto auloporoides, Nich., a portion of the polyzoary growing 
on Strophomena alternata, greatly enlarged. 2a. Portion of a 
branch of the same, still further enlarged, showing the biserial 
cells. 20. Portion of another branch, in which the cells are 
uniserial below and biserial above. 
Fig. 8. Alecto frondosa, James, a reticulated example, of the natural size, 
growing on Strophomena alternata. 3a. Portion of the same, 
enlarged. 36. Portion of the same, still further enlarged. 
3c. Portion of the polyzoary of another specimen, enlarged. 
3d. Portion of another specimen, enlarged, showing the minutely 
porous nature of the surface. 
Fig. 4. Alecto confusa, Nich., forming a crust on a crinoidal column, 
enlarged. 
Fig. 5. Aulopora arachnoidea, Hall, a specimen in which the branching 
is regular and no close reticulation is formed, growing on 
Chetetes gracilis, of the natural size and enlarged. 5a. Portion 
of a branch of the same, greatly enlarged. 
