POEIFEKA (sponges). 
41 
the cylindrical and branching examples of Dornderma 
(Fig. I G h) from near IVarminster. 
Xext follow the sponges from the Chalk, which, though 
perhaps more numerous, are not so well preserved. Those 
from the Upper Clialk of the South of England have had 
their skeletons almost entirely replaced by iron-peroxide; 
very frequently also they are now enclosed in nodules of 
solid dint, in part retaining their forms, but their interior 
structures are merged in the dinty matrix, and only show 
the course of the larger excurrent canals and the cloacal 
cavity. Such forms, commonly called Choanites, are 
repre.sented by the large collection of Toidmin Smith. 
In the sponges from the Upper Chalk of Flamborough, 
Yorkshire, the form is usually preserved, and also the main 
features of the canal system, but the spicular structure 
is now scarcely recognisable. Calcispongiae are repre- 
sented b}'’ Masmostonia and Pharetrosfongia, but are not 
numerous except in the case of the little globular Poro- 
sphacra. The Hexactinellida all belong to the Sub- Class 
Dictyonina, and among them the best known is the 
funnel-shaped Ventriculites with its folded walls (Fig. 10), 
but one should notice also the wide dange-like walls 
of Gnettardia and the mushroom-shaped Cocloptgchium. 
Among Demospongiae, the Choristid 
Tetractinellida are represented by 
Pachastrellu and >itelletta and numer- 
ous detached spicules of Gcodia (?). 
Lithistida are numerous, and here 
may be observed the large size and 
the projecting canal-openings in 
Stichophyma and Verruoulina from 
the Flamborough Chalk (Fig. 17). 
Monactinellida include the borings of 
Cliona in Molluscan shells. These 
last are the oidy representatives of 
springes in the British Tertiary series. 
Passing now to the fossil sponges from foreign 
localities, exhibited in the Wall-cases, one sees among 
the Ordovician specimens the large branching Lyssacine 
Hexactinellid, Brachiospunyia diyitata from Kentucky. 
; The Silurian of North America has furnished the 
Monactinellid Climacosponyia and numerous examjdes of 
the Lithistid genera Astylosponyia, Palaeomanon, and Hindia. 
The Lithistirl Aidocopium is from Gotland in the Baltic. 
Fig. 17 . — Vcrruculina 
licnssi. Senoniau 
Chalk of Flam- 
borough Head. J 
nat. size. 
Gallery X. 
Table-cases 
11 , 12 . 
Wall-case 
7a, 7b. 
Table-case 
11 . 
Wall-case 
8c. 
Wall-case 
8b. 
