90 REPORT— 1874. 
rated from one another by more or less conspicuous intervals near their calices. 
Septa alternately large and small, twenty-eight or thirty in number altogether, the 
primary ones nearly reaching the centre, the secondary ones marginal. Tabulze well 
developed, complete, about three in the space of one line. Increase by calicular 
gemmation, apparently in combination with parietal budding. 
Description of Species of Alecto and Hippothoa from the Lower Silurian 
Rocks of Ohio, with a Description of Aulopora arachnoidea. By H. At- 
tEYNE Nicuoison, M.D., D.Sc., F.RS.E. 
In this communication the author described the following fossils from the 
Hudson-River Group of South-western Ohio :— 
1. Hippothoa inflata, Hall, sp.—This is the Alecto inflata described by Hall from 
the older formation of the Trenton Limestone. Though in certain respects re- 
sembling some of the species of Alecto, the author expressed the opinion that this 
beautiful little species was an undoubted Hippothoa. The cells are pyriform, 
attenuated below, uniserial, and springing directly from one another, and the oval 
cell-mouths are placed on the front faces of the swollen cells. 
2. Alecto frondosa, James.—This species, named by Mr. U. P. James in his 
‘Catalogue of the Silurian Fossils of Ohio,’ was now for the first time described by 
the author. It forms anastomosing networks or thin expanded crusts parasitic upon 
Strophomena alternata. The cells are generally dispersed in two, three, or more 
rows, long and tubular, immersed below, but elevated towards the apertures, which 
are circular, terminal, and of the same diameter as the tube itself. 
3. Alecto auloporoides, Nicholson.—This is closely allied to the preceding, but is 
distinguished by its much more slender habit and graceful form, and by having 
its cells disposed in a double or single series. It presents a close superficial 
resemblance to Aulopora arachnoidea, Hall, from which, however, it can be readily 
distinguished. 
4, Alecto confusa, Nicholson.—This species forms thin crusts enveloping the 
columns of Crinoids. The cells are larger and more prominent than in the two 
preceding species, and are more closely and irregularly arranged. 
5. Aulopora arachnoidea, Hall.—The author gave a full description of this species 
for the purpose of separating it from Alecto auloporoides, which it closely resembles 
in external appearance. Though very similar to Alecto in many respects, it can be 
referred with considerable confidence to the genus Awlopora. 
Descriptions of New Species of Polyzoa from the Lower and Upper Silurian 
Rocks of North Ameria. By H. Attzynr Nicuwotson, M.D., D.Se., 
FRS.E. 
In this communication the author described the following new species of 
Polyzoa :— 
"2 Ptilodictya falciformis, Nich.—A large and beautiful form, allied on the one 
hand to Escharopora recta, Hall, and on the other hand to Ptilodictya lanceolata, 
Goldfuss, P. gladiola, Billings, and P. sulcata, Billings. oc. Cincinnati Group, 
near Cincinnati, Ohio. 
2. Ptilodictya emacerata, Nich.—A minute species allied to P. fragilis, Billings, 
from strata of the same age in the island of Anticosti. Loc. Cincinnati Group, 
Ohio. ; 
3. Ptilodictya flagellum, Nich.—A species belonging to the same group as 
P. gladiola, Billings, and P. falciformis, Nich., but distinguished by its much 
eS size, less width, and flexuous form. oc. Cincinnati Group, Lebanon, 
hio. 
4. Ptilodictya? arctipora, Nich.—It is doubtful if this curious species is a true 
Ptilodictya, but it presents some affinity with P. raripora, Hall, from the Clinton 
Group. Loc. Cincinnati Group, Cincinnati, Ohio. 
5. Ptilodictya fenestelliformis, Nich.—This in some external respects might readily 
