262 PLATE LXXXI. 



and tlie greater portion have a slight inflation near the 

 middle of the shaft. The distinction in size between 

 these spicula and those of the skeleton is very remark- 

 able- The skeleton spicula of an average size is -^ inch 

 in length, and g^-g- in diameter, while a medium-sized 

 tension spiculum measured y^-g inch in length and 



- inch in diameter. 



5174 



The retentive spicula are of two distinctly different 

 sorts. The largest form are simple attenuato-stellate 

 spicula, with but few long and slender radii, and they 

 are three or four times as large as the smaller ones, 

 which are almost all of them elongo-attenuato-stellate 

 in form, and are very much more abundant than the 

 larger ones. 



A few gemmules were found amidst the skeleton 

 tissues ; they were of the usual halichondroid form, 

 membranous and aspiculous. 



In the course of my examination of a number of small 

 sponges from 96 fathoms Shetland sent to me by Mr. 

 Norman, I found one little packet containing five small 

 specimens of a milk-white colour. The largest is one 

 and a quarter inch in length, half an inch in width, and 

 about two lines in thickness ; they all prove to be 

 young specimens of Normania crassa the smallest of 

 them exhibiting the characteristic structural pecu- 

 liarities of the species in perfection; the general 

 arrangement of the skeleton, and every form of spicu- 

 lum being as fully and completely developed as in the 

 type-specimen of the genus. These little coating 

 specimens of the sponge are strikingly illustrative of the 

 futility of the characters of form and colour in the 

 descriptions of sponges. 



