Prof. W. Thomson on the “ Vitreous” Sponges. 119 
Suborder 3. (Halichondrida) Sponerna (Lieberkiihn). Ske- 
leton an elastic wide-meshed network of anastomosing horny 
fibres, frequently containing foreign bodies, such as grains of 
sand and spicules of other sponges, and occasionally siliceous 
spicules developed within them, and never associated with free 
siliceous spicules in the sponge-mass. Ex. Spongia, Chalina, 
Dysidea, 2 
Order 3. (P. Silicea) CorticaTa (O, Schmidt). Globular, 
tuberous, or branched Sponges, supported by regular radiating 
sheaves of long siliceous spicules, and invested with a special 
dense cortical layer, often containing spicules of special and 
characteristic forms. Ex. Tethya, Geodia, Placospongia. 
Order 4. (P. Silicea) ARENOSA (= Arenospongia, Gray). 
“Sponge consisting of a disk of agglutinated sand, with a 
series of diverging spicules on the circumference of the disk, 
and a pencil of similar spicules at the mouth of the oscules on 
the upper surface of the disk.”’ (Gray,7.c.) Ex. Xenospongia. 
Order 5. (P. Silicea) HAuisarcina (Lieberkiihn). Sponge 
an extended sheet of sarcode, destitute of either siliceous or 
horny support. Ex. Halisarea. 
My principal object in the present communication is to de- 
fine the first of the siliceous orders, the glassy Sponges. I 
believe the following to be the scope of the group in known 
genera and species :— 
Order I. (Porifera Silicea) VITREA. 
Genus 1. HABRODICTYON*, n. g. 
H. speciosum, Quoy & Gaimard (sp.). 
H. corbicula, Valenciennes (sp.). 
Genus 2. HyALONEMA, Gray (in part). 
H. Sieboldi, Gray. 
H, lusitanicum, Gray. 
~ Genus 3. EUPLECTELLA, Owen. 
E. aspergillum, Owen. 
Genus 4. APHROCALLISTES, Gray. 
A. beatrix, Gray. 
Genus 5. DAcTYLOCALYX, Stutehbury. 
D. pumicea, Stutchb. - 
D. subglobosa, Gray. 
D. Prattii, Bowerbank. 
D. callocyathes, Gray (sp.). 
D, azorica, Gray (sp.). 
D.? torva, Duchass. & Michelotti (sp.). 
Genus 6. FARREA, Bowerbank. 
fF. occa, Bowerbank. 
* ABpos, delicate, and Sixrvoy, a net. 
+ Through the kindness of Dr, Farre, Ihave had an opportunity of see- 
