BEITISH SPONGIADjE. 205 



I have carefully examined the type specimen of Dr. 

 Johnston's Halichondria carnosa, which is in the British 

 Museum, and I find that the spicula of the skeleton, 

 although agreeing in form with those of H. suberea, are pro- 

 portionally much more slender and considerably longer, but 

 as I have entered fully into the details of these characteristic 

 differences existing between the two species, I will not repeat 

 them here, but refer the student to my account of them in 

 the description of the differential characters of the two 

 species under consideration as the best mode of discriminat- 

 ing them under doubtful circumstances. 



I am indebted to my late friend, Mr. John Howard 

 Stewart, of the Royal College of Surgeons, for four speci- 

 mens of this species on a broken shell of Pecten opercularis. 

 Two are about half an inch in diameter, one about two lines, 

 and the fourth very little more than a line. They are all 

 nearly globular, and completely sessile. Another specimen 

 from the same gentleman is also sessile, the base embracing 

 the point of a Dentalium. 



In a pear-shaped specimen, ten lines in height and eight 

 in diameter, that I received for examination from the Rev.. 

 A. M. Norman, there vpere an abundance of dark amber- 

 coloured spherical vesicles, filled with round or oval mole- 

 cules ; the whole mass of the sponge, excepting a space 

 about equal to the length of a skeleton spiculum below the 

 dermal membrane, appeared to be crowded with them. 

 They were dispersed without any approach to order, and the 

 fully-developed ones were nearly of the same sizej an 

 average-sized one of this description measured ^joth of an 

 inch in diameter. The parietes of the vesicle consists of a 

 simple, strong, transparent, aspiculous membrane, and each 

 of the molecules within it appeared to have a distinct trans- 

 parent membranous envelope. I could not with a linear 

 power of nearly 600 detect a foramen in any of these vesicles, 

 but from their structure and mode of disposition within the 

 sponge I have no doubt of their being its reproductive 

 gemmules. 



The Rev. A. M. Norman found this species at Durie Voe, 

 Shetland. He says : " The amount of animal matter in 



