48 
SILURIAN 
fossils, and as the genus is only named, not described in the 
paper quoted below, I will give its characters here. It is, so 
far as I know, a truly Silurian form, and it is another link 
between these Indian strata and our own. The Thibet speci¬ 
mens show the structure remarkably well. 
SPHiEROSPONGIA.- New Getius. 
Ovoid or pyriform masses, hollow within, the parietes con¬ 
sisting externally of convex regular hexagonal or rhomboidal 
mammillae, with sinuous margins; the sinuations with salient 
and retreating angles, and often produced into short processes. 
Internally [in the Devonian species] the walls are strengthen¬ 
ed by longitudinal bars or ribs. 
It is possible that the smaller species which has rhomboidal 
areolae so arranged as to resemble the engine-turning on the 
back of a watch, may be of another genus allied to Ischadites . 
This last (Ischadites) is a true regular sponge with roots, 
and has nothing to do with the Cystidece , to which it was 
formerly supposed to be allied. 
I have almost as little doubt that the strange genus Nidu- 
Utes , found in middle Silurian rocks in Britain, is a sponge 
somewhat allied to these forms. But as that occurs in the 
form of flattened plates, with honeycomb openings on both 
sides, it cannot be a very close ally. 
SPH, MELLIFLUA. 
Plate 5, figs. 4, 5, 6. 
An ovoid mass, about one inch and a half long, and an inch 
broad, very convex , covered with long hexagonal areolae, only 
slightly convex, and rather less than a line broad, rugose, but 
without any central mammilla : their edges sinuate,—only 
minutely so in some cases,—in others, fig. 4 a , produced into 
long processes. 
The convexity and size of the areolae in this striking species, 
which appears to be common enough in certain beds of the 
