322 DR. J. S. HOWERBANK ON THE SPONGIAD.E. [Mar. 18, 



drical. Interstitial membranes — spicula the same as those of the 

 dermis, comparatively few in number. 



Colour, dried, light ochreous yellow. 



Hab. Nichol Bay, Australia (Mr. George Clifton). 



Examined in the dried state. 



This remarkable specimen of Dietyocylindrus is 17^ inches in 

 height, and its greatest breadth 7 inches ; the branches appear all 

 to have maintained their natural position, and several of them near 

 the distal termination of the sponge are united by inosculation. 

 The natural base has been preserved. The pedicel is stout and 

 short, and it does not rise from the base quite 3 inches before it is 

 resolved into numerous ascending branches, which divide dichoto- 

 mously or trichotomously. Each of the branches is furnished with 

 numerous stout compressed tooth-shaped processes, consisting of 

 converging compressed masses of skeleton-spicula pullulating from 

 the axial skeleton of the branch, and entirely enveloped by the 

 coriaceous dermis. The most decisive specific character of this 

 sponge is undoubtedly the singular forms of spicula that abound in 

 the dermal membrane, the dentato-cylindro-hexradiate defensive and 

 retentive spicula. The membrane is crowded with them in all parts. 

 From the shortness of their radii allowing them to assume any 

 imaginable position, when mounted for examination their normal 

 form is not always to be readily recognized ; but a careful observation 

 soon establishes the true nature of their structure. In nearly all of 

 them the number of the dental terminations of the radii vary ; but the 

 tridentate terminations appear mostly to predominate. Abnormal 

 variations in the forms of these spicula are by no means infrequent. 



The axial skeleton of the branches fills the whole of their 

 diameter, and has all the characters of a true Dietyocylindrus. It 

 is rather compactly constructed ; and a few slender spicula, of the 

 same form as those of the skeleton, are interwoven at various angles 

 with those of the great ascending column. The true structure of 

 this sponge can be exhibited only in a longitudinal section. 



Ecionemia acervus, Bowerbank. (Plate XXX.) 



Sponge massive, pedicelled (?) ; surface even, minutely hispid. 

 Oscula simple, dispersed, few in number. Pores inconspicuous. 

 Dermal membrane furnished abundantly with subtuberculated fusi- 

 formi-cylindrical spicula, very minute and short. Connecting-spicula 

 attenuato-expando-ternate, large, stout, and abundant, and with a 

 considerable number of attenuato-recurvo-ternate spicula ; shafts long, 

 slender, and attenuated. Skeleton — spicula of axis fusiformi-acerate, 

 very large and stout. Interstitial membranes — tension-spicula ace- 

 • rate, minute, and slender, numerous, and tuberculated fusiformi-cylin- 

 drical, short and stout, very minute, numerous. Retentive spicula 

 subsphero-attenuato-stellate; radii few and very slender, and cylindro- 

 sphero-stellate radii short and numerous ; both forms very minute. 



Colour in the dried state dark brown. 



