242 Description of new Lower Silurian Sponges. — JJlrich. 
*" osculum " at the center of these areas. Again, over limited 
spaces canal apertures may be wanting. 
In the number of canals in a given space this species agrees 
very nearly with H. knotti. Still, the more irregular growth, 
remarkably rough surface, and absence of oscula serve very 
well in distinguishing them. 
Formation and locality : Upper beds of the Cincinnati 
group, in Marion and Lincoln counties, Kentucky. 
SACCOSPONGIA, n gen. 
Sponges simple, of sub-cylindrical or oval form, with a cen- 
tral cloacal cavity extending through the sponge from its sum- 
mit to the base. Walls moderately thick, very porous, being 
traversed by large, tortuous, branching canals, intercommuni- 
cating freely with each other. Minute characters of skeleton, 
robably similar to that of Heterospongia and Dystacto- 
spongia. A dermal layer of compact structure is developed 
over at least the basal portion. 
Type : S. 7'udis, n. sp. 
This genus is believed to differ from Heterospongia and 
Dystactospongia mainly in its mode of growth and in pos- 
sessing a cloacal cavity. 
SACCOSPONGIA RUDIS, n. sp. 
Sponge of sub-ovate form, or with the sides parallel and the 
two extremities rounded, the upper, however, slightly truncate. 
A rather small but nearly complete example is 65 mm. long by 30 
mm. wide. The cloaca, about 18 mm. in diameter, extends down- 
ward apparently to the base. Outer surface roughly and very 
irregularly pitted, or lined with tortuous ridges. The latter 
occur on the lower portion of the sponge mainly. Channels 
between the ridges porous, the openings small, sub-circular or 
transversely elongated, and often ranged in series. Canal 
openings oblique, very unequal, their width varying between 
the extremes of 1 and 3 mm. Walls separating canals porous, 
usually 0.5 or 0.6 mm. thick. A thin dermal layer, seemingly 
composed of very minute and closely interwoven spicules, 
covers a portion of the base of one of the examples. 
All the specimens have been distorted through compression, 
and much of the variation of form noticed is obviously due to 
that cause. 
Formation and locality : In the siliceous beds at the top of 
the Trenton, near Lexington and Frankfort, Kentucky. The 
