76 DR.J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Jan. 28, 
When the expansile dermal system is present wholly or in part 
in specimens under examination, we are enabled to establish specific 
characters of external form and structural peculiarities of the most 
satisfactory description ; but when that important portion of the 
organic structure of the sponge is absent, the characters derived from 
the form and surface of the rigid skeleton are necessarily provisional, 
and can maintain their places in its description only until a specimen 
in a natural and perfect state can be procured. When in the denuded 
state, the form and surface of the sponge should be stated as those 
of the rigid skeleton, not as that of the sponge. 
Genera. 
DactyLocatyx, Stutchbury. 
Skeleton siliceo-fibrous. Fibres solid, cylindrical. Reticulations 
unsymmetrical. 
Type Dactylocalyx pumiceus, Stutchbury, P. Z. 8. 1841, p. 86. 
IpnHirEoNn, Valenciennes. 
Skeleton siliceo-fibrous. Fibres solid, cylindrical. Reticulations 
symmetrical. Areas rotulate, confluent. 
Type Iphiteon panicea, Museum Jardin des Plantes, Paris, from 
Porto Rico, 1799. 
Myuivsia, Gray. 
Skeleton siliceo-fibrous. Fibres solid, cylindrical. Rete sym- 
metrical, disposed in a series of crypt-like layers parallel with the 
external surface, with intervening planes of perforated siliceous 
tissue. 
Type Myliusia callocyathes, Gray, from the Island of St. Vin- 
cent, P. Z. S. 1859, p. 439, and 1867, p. 506. 
Katiapvsis, Bowerbank. 
Skeleton siliceo-fibrous. Basal fibres cylindrical and canalicu- 
lated ; distal fibres non-canaliculated, compressed. Basal reticula- 
tions symmetrical and reversedly arcuate; distal reticulations un- 
symmetrical and continuously ramifying. 
Type Kaliapsis cidaris, Bowerbank. 
Farrea, Bowerbank. 
Skeleton siliceo-fibrous. Fibres canaliculated, canals continuous. 
Rete symmetrical ; interstices rectangulated. 
Type Farrea occa, Bowerbank. 
PuristpHonia, Bowerbank. 
Skeleton siliceo-fibrous. Fibres canaliculated, canals continuous. 
Rete unsymmetrical. 
Type Purisiphonia Clarkei, Bowerbank. 
