378 A MONOGRAPH OF THE 



bedded ones are projected at various angles, in an upward 

 direction, thus assuming the office of internal defensive 

 spicula. The secondary fibres of the skeleton are usually 

 aspiculous, solid, and cylindrical, and from about the 

 middle of the greater portion of them there is a single 

 auxiliary defensive spiculum, projected in an outward 

 direction ; the spicula have their bases firmly imbedded in 

 the keratose fibre, from which they emanate. The internal 

 defensive spicula are not equally abundant in every speci- 

 men of the species. In one from the coast of Cornwall, 

 which completely enveloped the stem of a large Fucus 

 nearly an inch in diameter, for about three inches of its 

 length, they were remarkably few in number, many of the 

 primary lines being destitute of them ; the thickness of the 

 sponge did not exceed the eighth of an inch. The inter- 

 stitial membranes do not appear to exist in an equal degree 

 in all parts of the interior of the sponge, but when present, 

 they are rather abundantly furnished with the two forms of 

 tension spicula described above. 



Ophlitaspongia, Bowerbank. 



1. Ophlitaspongia papilla, Bowerbank. 



Sponge. Sessile, massive ; surface papillated, hispid. 

 Oscula simple, on the apices of the papillae. Pores 

 inconspicuous. Dermal membrane pellucid, spiculous, 

 spicula fusiformi-attenuato-acuate, rather slender; 

 and tricurvate acerate, variable in size, numerous. 

 Skeleton. Fibre stout and strong; rete compact; 

 somewhat irregular ; spicula fusiformi-attenuato-acuate, 

 short and stout, numerous, projected from the sm-- 

 faces of the fibres at various angles to their axes. 

 Interstitial membranes spiculous ; spicula same as 

 those of the dermal membrane. 



