AEA Pharetrond Sponge from Christmas Island. 131 
body-skeleton of Murrayona seem to me very strong. In the Lithonine 
sponges Petrostroma schulzer, Dod., and Minchinella lamellosa, Kirkp., the firm. 
skeletal network is constructed of large four-rayed spicules cemented 
together. In the older parts of the skeleton the calcareous cement becomes 
more and more developed, so that it is difficult to trace the spicules in 
the thick strands of the network. 
In fact the rdle of the cement becomes increasingly important, and that 
of the axial core of spicules practically negligible. As the cement became 
more rapidly and abundantly deposited, it would become increasingly 
difficult for the enclosed scleroblasts to retain their functions. 
The dermal scales may have arisen owing to the tendency of so many 
Pharetronid sponges to form wrinkles and folds, a tendency so marked 
that Zittel (10, p. 63) gives it in his diagnosis as one of the characters of the 
group—‘“a smooth or corrugated dermal layer frequently present.” Sometimes 
the wrinkles are concentric. The tendency to form these calcareous surface- 
plates may be correlated with the richness of the sponge in cement-building 
cells. 
Murrayona is of interest to the paleontologist, because he must take into 
consideration the possibility that some fossil Pharetrones, in which he has 
been unable to detect spicules, may never have possessed them. Hitherto, 
the absence of spicules has been attributed to fossilisation, and this may be 
the true cause in many instances, especially in those cases where the spicules 
are found in some parts of the sponge and not in others. 
In Corynella (Myrmeciwm) gracilis, Minster, the skeletal network consists 
of thin anastomosing fibres, in which neither Zittel nor Hinde have been able 
certainly to recognise spicules, though certain wavy lines and other doubtful 
markings were regarded possibly as being spicules. Zittel (9, Plate 12, 
fig. 5) gives a figure of a section of C. gracilis, showing the fibres with 
spheroidal rayed crystalline structure. The fibres of Murrayona have fan- 
shaped or circular groupings of fibrillar markings, rather than spheroidal 
(Plate 11, fig. 16). | 
The diagnoses of the new sub-family, genus and species, are as follows :— 
Sub-family Murrayonine (n. sub-fam.), Pharetronide with a firm main 
skeletal network entirely devoid of spicules. 
Murrayona (n. gen.), Murrayonine with a dermal covering of scales. 
Murrayona phanolepis, n. sp. With solely triradiate spicules, and with the 
poral area limited to a semicircular equatorial groove. 
The six known recent species of Pharetronide are the following :— 
