1873.] DR. J. S. BOWERBANK ON THE SPONGIADjE. 331 



fusiformi-acuate or subovo-spinulate, very large and long. Skeleton, 

 spicula superfusiformi-acuate and subovo-spinulate, large and long- 

 Tension-spicula superfusiformi-subovo-spinulate, small, irregularly 

 dispersed, numerous. 



Colour, dried, light grey. 



Hab. Portland, Maine, N. America (Dr. Dawson, M'Gill's Col- 

 lege, Montreal). 



Examined in the dried state. 



I received a small slice of this sponge from Prot. Dawson. From 

 the curve of the surface, this specimen appears to have been about 

 an inch and a half in diameter. In its present state the hispidation of 

 the surface is very strongly produced, and probably much exaggerated 

 by drying ; the spicula are comparatively very large and long — more 

 so than those of the skeleton-fasciculi. The secondary series of de- 

 fensive spicula are of the same form as those of the interstitial mem- 

 branes, but not more than half their average size. The whole of the 

 spicula are exceedingly fusiform, the middle of the shaft being fre- 

 quently twice the diameter of the base of the spiculum. The ovo- 

 spinulate character prevails more or less in all the spicula, but is 

 more distinctly produced in those of the interstitial membranes and 

 the secondary dermal defensive ones. In the deeply seated portions 

 of the skeleton- fasciculi the ovo-spinulate character is very nearly or 

 quite obsolete in some of the skeleton-spicula, and in others every 

 gradation of its development may be traced up to its perfect produc- 

 tion. No traces of reproductive organs could be detected on any 

 part of the interstitial membranes. 



The peculiarities of the organization of this sponge distinctly 

 separate it from any other species with which I am acquainted. 



DESCRIPTION OF THE PLATES. 

 Plate XXVIII. 

 Isodictya mirabilis, Bowerbank. 

 Fig. 1 represents the type specimen, natural size. 



2. A small portion of a section at right angles to the dermal surface, mag- 



nified 80 linear. 



3, 4. Two of the short, stout acuate skeleton-spicula, magnified 123 linear. 



5. One of the slender tension-spicula from the interstitial membranes, mag- 



nified 123 linear. 



6. One of the inhalant pocilla, partially closed by the radial arrangement of 



conical sacculi, magnified 61 linear. 



7. A section at right angles to the dermal surface of one of the inhalant 



pocilla, magnified 61 linear. 



8. One of the conical sacculi of the inhalant areas, exhibiting the remains 



of a membi-ane, which probably occasionally closed the mouth of that 

 organ, magnified 80 linear. 



Plate XXIX. 

 Dictyocylindrm dentatus, Bowerbank. 

 Fig. 1 represents the type specimen, half the natural size. 

 One of the branches, natural size. 



A side view of one of the dentato-cylindro-hexradiate retentive and de- 

 fensive spicula from the dermal membrane, magnified - r >."0 linear. 



•> 



