On Species of Hippothoa and Alecto. 123 
~XV.—Descriptions of Species of Hippothoa and Alecto from 
the Lower Silurian Rocks of Ohio, with a Description of 
Aulopora arachnoidea, Hall. By H. ALLEYNE NICHOLSON, 
M.D., D.Sc., F.R.S.E., Professor of Biology in the College 
of Physical Science, Newcastle-on-Tyne *. 
[Plate XI.] 
THE fossils upon which the followingcommunication is founded 
were in the first place kindly submitted to me for examination 
and description by Mr. U. P. James, of Cincinnati, an ac- 
complished and experienced observer, and a studious worker 
in the richly fossiliferous Silurian strata of the State of Ohio. 
Subsequently I had the opportunity of visiting Ohio personally, 
and I obtained a large additional series of these forms at Cin- 
cinnati and at Waynesville. They constitute a small group 
of organisms which may be advantageously considered to- 
gether, though differing considerably in their nature. ‘The 
first of them is the Alecto inflata of Hall, which is an un- 
doubted Polyzoon, though certainly referable to another genus. 
T have examined very carefully a number of beautifully pre- 
served specimens, and am able to give a more complete descrip- 
tion of its characters than has yet been published. Three 
species (viz. A. frondosa, A. auloporotdes, and A. confusa) 
appear to me to be undoubted examples of Alecto, and they 
all would seem to be new. Lastly, I have appended a descrip- 
tion of Aulopora arachnoidea, Hall, because this form, whilst 
seeming to be a genuine Aulopora, presents certain striking 
points of resemblance to Alecto auloporoides, with which it 
might readily be confounded. 
1. Hippothoa inflata, Hall. Pl. XI. figs. 1, 1a. 
Alecto inflata, Hall, Pal. N. Y. vol. i. p.77, pl. xxvi. figs. 7 a, 7 6. 
Polyzoary creeping, adnate, branched, and forming a close 
but irregular network. Branches linear ; cells uniserial, pyri- 
form, each springing by a contracted base directly from the 
cell below ; about four cells in the space of one line. Cell- 
mouths smaller in diameter than the expanded end of the cell, 
subterminal, and placed more or less distinctly on the front 
face of the cell. 
Though in some respects resembling some of the species of 
Alecto, | think there can be no hesitation in referring this 
beautiful species to the genus Hippothoa, with which it agrees 
* Communicated by the Author, having been read at the meeting of 
the British Association at Belfast, before Section C. 
