138 ARTHUR DENDY. 
fectly known, and even their calcareous nature has been dis- 
puted. This was largely owing to the fibrous character of the 
skeleton, which was not then known to occur in any living 
calcisponge, and certainly appeared to indicate a siliceous 
nature for the Pharetrones. 
In 1882, however, Dr. Hinde published a valuable paper (5) 
in which this question was fully discussed, and described more 
or less in detail the spiculation of five species of so-called 
Pharetrones from the Cretaceous and Upper Greensand forma- 
tions. These observations sufficiently proved the calcareous 
nature of at any rate these five species, for characteristic tri- 
radiate and quadriradiate spicules were detected. 
The first species described by Dr. Hinde is Verticillites 
d’Orbignyi. The description and figures clearly prove this 
to be a calcareous sponge, but I do not think that there is the 
slightest evidence in favour of regarding it as a Pharetronid. 
It is a very thin-walled sponge, and the portions of the skeleton 
described are evidently simply the dermal and gastral cortex 
respectively. The latter is very strongly developed and differs 
in no essential respect from that of many living Heteroccela, 
being composed of a dense feltwork of triradiate spicules with 
aborted basal rays. This layer is pierced by the circular ex- 
halant apertures leading into the gastral cavity, which, being 
placed near together, give the gastral cortex a reticulate cha- 
racter. To apply the term fibrous to this skeleton appears to 
me to be a mistake; it is no more fibrous than that of many 
living Heteroceela, and the so-called fibres are certainly not 
homologous with the spicular fibres of Lelapia. Verti- 
cillites d’Orbignyi ought, then, to be removed from the 
Pharetrones altogether. The thinness of the sponge-wall 
and the regular disposition of the exhalant openings on the 
gastral surface suggest that it may have possessed a Syconoid 
canal system, while the presence of quadriradiates in the 
dermal cortex, with inwardly projecting apical rays, suggests 
a position amongst the Amphoriscide of my classifica- 
tion. 
In the next two species, again, Corynella rugosa and C, 
