Gallery, 
No. 10. 
Table-cases, 
Nos. 9, 10. 
Graptolites. 
Wall-case, 
No. 6. 
Table-case, 
No. 10. 
Spongres. 
86 Hydrozoa and Spongida. 
of England, and the genera Syringosphceria and Stoliczlcana 
from India. 
In the Hydrocoral linj: are placed the Silurian genus 
Labechici, the Devonian and Silurian types of Stromatopora, and 
the Cretaceous and Tertiary Millepora. 
The last division of the Hydrozoa contains the Graptot.i- 
thinj}, a remarkable Palseozoic group characterised by the 
possession of a compound polypary with a tubular chitinous 
covering enclosing the coenosarc, and supporting numerous cup- 
like “ cellules ” or Jiydrothecce , in each of which a polypite was 
placed. The polypites were united to the coenosarc. The 
polypary itself, which was apparently free and unattached, was 
strengthened by a chitinous rod or fibre termed the solid axis, 
no doubt similar to that observed in the polyzoon ffliabdopleura. 
The Graptolites present a great variety in their form and in the 
arrangement of the hydrothecce on the axis, some having but a 
single row of closely-placed “cellules” or hydrothecce on each 
branch (hence called “ monoprionidian Graptolites”), others 
having a row of cellules on each side of the branch (hence 
called “ diprionidian ”). These forms of Graptolites (dip ri- 
onidian) are, with hardly an exception, confined to the Ordo- 
vician series, whilst the monopnonidian forms range from the 
base of the Ordovician to the summit of the Silurian series. 
With the exception of the genus Dictyograptus , which sur- 
vived to the Devonian, the Graptolites are confined to the 
Cambrian, the Ordovician, and the Silurian. 
The families, genera, and even the individual species, of 
Graptolites are, according to Prof. Lap worth, remarkably 
characteristic of special zones in the Silurian, and that 
apparently over extremely wide areas of the earth’s surface. 
The exhibited series of this interesting and important group 
of Palaeozoic Hydrozoa is placed in Table-case No. 10 and Wall- 
case No. 6. 
Sub-Kingdom. — PoRIFERA. 
Class 21. — Spongida (Sponges). 
The Sponges form the lowest group of coelenterate animals. 
With the exception of one small division, the Myxospongice , 
whose structure is entirely composed of soft, fleshy substance, 
sponges secrete hard skeletons, either of horny siliceous, or 
calcareous materials, and they have consequently been divided 
into Ceratospongire, Silicispongice , and Calcispovgice. It is very 
doubtful if any of the Keratose, or horny sponges, similar to 
those in domestic use, have been preserved in the fossil state, 
