234 A MONOGRAPH OF THE 



The specimen in course of description is but a fragment 

 of the perfect sponge. It is one inch in length, half an 

 inch broad, and four lines in thickness, and in its present 

 state it is exceedingly friable. The dermal membrane 

 presents excellent specific characters ; the unispiculous net- 

 work is irregular in its area, but uniform in its general 

 character ; the spicula forming it are not united at their 

 apices, but they cross each other at various angles, forming 

 triangular and quadrangular spaces, the sides of which are 

 less in length than the spicula bounding them. When the 

 sarcode is well preserved, the minute acerate, and sub- 

 angulated tricurvate acerate spicula are abundantly dis- 

 persed, the latter being much more numerous than the 

 former. The sub-angulated spicula are remarkable in 

 their character, the central curve in the greater portion of 

 them is so abrupt as to frequently cause the spiculum to 

 assume the form of a right angle, while the terminal curves 

 are but very slightly produced ; but this extreme angula- 

 tion, although it obtains to a considerable extent, is not 

 universally prevalent, and others may be found exhibiting 

 the usual variations in form and curvature that occur among 

 this form of spicula. The same descriptions of tension 

 spicula occur on the interstitial membranes, but apparently 

 not to so great an extent as on the dermal one. 



The specimen described is the only one of the species 

 I have seen. It was sent to me among the sponges dredged 

 off Guernsey by the Rev. A. M. Norman. I do not recol- 

 lect to have seen tricurvate spicula in any other sponge 

 of the first section of Halichondria. 



4. Halichondria caduca, Bowerbank. 



Sponge. Massive, sessile, surface rugged. Oscula simple, 

 dispersed. Pores inconspicuous. Dermal membrane 

 spiculous, spicula same as those of the skeleton, dis- 

 persed, numerous, and a few acerate, very slender. 

 Skeleton diffuse, and very irregular; spicula sub- 

 fusiformi acerate, rather stout and long, rarely acuate. 



