166 Cincinnati Society of Natural History. 
SPATIOPORA ASPERA, n. gen. et. sp. (PI. VII., figs. 5, 5a and 50.) 
(gen. char. ante vol. v., p. 159. 
Zoarinum parasitically attached to the shells of Orthoceras, over 
which it forms large, but very thin expansions, uever, so far as 
observed, exceeding .05 of an inch in thickness. Cells oblong, of very 
irregular shapes, more or less unequal in size, with an average diameter 
of j.th of an inch. At intervals of about .15 of an inch the surface 
exhibits clusters of larger cells, some of which may attain a diameter 
of jth of an inch, These groups are not so conspicuous on account 
of their size, as for the aggregation of the remarkably developed spini- 
form tubuli, which, being also distributed between the ordinary cells, 
give the entire surface a very rough appearance. The cell-walls when 
not enlarged by the spiniform tubuli are thin. 
Longitudinal sections (Pl. VII., fig. 5b) are remarkable for the very 
unequal thickness of the cell-interspaces. ‘This peculiarity is due to 
the fact that on one side of the tube the divisional wall is simple and 
thin, while on the other side it may be much thickened by one of the 
spiniform tubuli. Diapbragms appear to be wanting. 
In tangential sections (PI. VII., fig. 5a) the cell-walls are of variable 
thickness, and traversed by peculiar interrupted, dark streaks, that 
give these sections a marked resemblance to similar sections of the 
Lower Silurian Ceramoporide. The walls of adjoining. tubes are 
apparently fused with one another. The cell-cavities are irregularly 
shaped, and often indented by an inflexion of the wall. 
The genus Spatiopora is established to receive seven Lower 
Silurian species. Four of these are now described for the first time, 
the fifth was described and figured by Edwards and Haime in 1850, 
under the name of Chetetes tuberculatus, the sixth is about to be 
published by Mr. Arthur Foord in the next publication of the 
Canadian Survey; while the seventh must for a time remain unpub- 
lished. The affinities of the genus are directly intermediate between 
the Ceramoporide and Monticuliporide, the external appearance of 
the cells and zoarium in general being like that of other parasitic 
genera of the latter, while the internal structure of the walls is pre- 
cisely like that of the most typical species of the former family. To 
decide to which of these two families the genus most properly belongs, 
can not, at this time, be done with any certainty, and as I have not 
yet figured any of the Ceramoporide, I will postpone my comparisons, 
until I shall have done so. 
S. aspera, the type of the genus, is easily distinguished from this 
species by its rough surface. 
Formation and locality: Cincinnati group. Comparatively rare at 
