156 A MONOGRAPH THE 



The form of this sponge is nearly circular, the diameter 

 being about two and a half inches. It is so much de- 

 pressed that it does not exceed half an inch in thickness. 

 There are two smooth spaces on the under side, about 

 three eighths of an inch in diameter, which have apparently 

 been points of adherence to a smooth surface. The re- 

 mainder of the inferior portion is much like that of the 

 superior one, excepting that there are no oscula apparent, these 

 organs being confined to the upper surface and margin of 

 the sponge ; they are dispersed about an inch apart, and 

 the largest rather exceeds two lines in diameter. The 

 pores are apparent to the unassisted eye ; they are com- 

 paratively not very numerous. The spicula of the skeleton 

 are stout and slightly curved, and are comparatively by no 

 means abundant ; while those of the membranous structures 

 are exceedingly numerous ; the latter are slender and 

 slightly curved. The dermal membrane is abundantly fur- 

 nished with the slender spicula, intermixed with a small 

 number of the larger ones. The interstitial membranes are 

 crowded with the slender spicula, irregularly felted together, 

 as it were, amid which the skeleton spicula are dispersed 

 at intervals, singly or in small groups, comparatively con- 

 siderable spaces in the membranes being without them. 



At the first view dried specimens of this species may be 

 readily mistaken for //. caruncula, the rugose surface being 

 very similar to that of the latter species. 



I am indebted for this sponge and many other valuable 

 specimes to the liberality and kindness of my friend Capt. 

 F. W. L. Thomas, R.N., who has done so much to advance 

 our knowledge of marine natural history during his services 

 as commander of the Hydrographical Survey in the Orkneys, 

 Shetland, and the Frith of Forth, and in commemoration of 

 which I have much pleasure in attaching his name to this 

 new and interesting species. 



2.Hymeniacidon coccinea, Boioerbank. 

 Sponge. Amorphous sessile. Surface uneven, rugged. 



