192 A MONOGRAPH OF THE 



tato-palmate ones, but they are of the same size, and are 

 indiscriminately mixed with them in the radial groups. 



The next most remarkable feature in this interesting- 

 sponge is the comparatively enormous size of the deflected 

 and contort bihamate spicula, which are of such dimensions 

 that a single one would span a whole group of the anchorate 

 ones ; they are attached by their points to the membrane, 

 while their curved shafts are thrown upward amidst the sar- 

 code. They are very few in number, and are widely dis- 

 persed. 



The small simple bihamate spicula are much more nume- 

 rous than the large ones, and are as remarkable for their 

 minuteness as the larger ones are for their great size : with- 

 out the aid of a power of about 400 linear, they can scarcely 

 be detected in situ, although the specimen be immersed in 

 Canada balsam, and it must be remembered that without 

 this mode of preparation even the radial groups will not be- 

 come visible. 



I subsequently received a second specimen of this sponge 

 from Professor Dickie, of Queen's College, Belfast, and this 

 one also was on a shell of Pecten opercularis. It occupied 

 about half an inch in width of the whole front of the shell, 

 while the remainder of the valve was covered with Hali- 

 chondria nigricans. The essential characters of this speci- 

 men of Hymeniacidon Jloreum were in accordance with those 

 of the first, but in the part examined the rosette-like groups 

 of spicula were very few in number. The specimen being 

 young and very thin may probably account for the difference 

 between the two in this respect. 



There are some peculiarities in this species which might 

 readily mislead a hasty observer into the belief that it was 

 a variety in form of Hymeniacidon lingua. Thus the 

 strikingly characteristic groups of retentive spicula resemble 

 each other in both form and mode of arrangement so closely 

 that if it were not that they are rather less than half the 

 diameter in H. Jloreum, of those in H. lingua, it would be 

 difficult to distinguish one from the other. The spicula of the 

 skeleton also rather closely resemble each other, but those of 

 II. Jloreum differ from the skeleton spicula of H. lingua in 



