144 A MONOGRAPH OP THE 



I have to thank my friend, Mr. Barlee, for this new 

 species. He took two specimens at Shetland during his 

 deep sea dredging at that locality, in 1858. One coats a 

 portion of the outer surface of a valve of a dead shell of 

 Astarte Scotica, covering a space of about eight lines in 

 diameter. It is exceedingly thin, and, in the dried state, 

 can only be distinguished from the dark periostracum of 

 the shell by the grains of extraneous matter which are 

 abundant on its surface, and by the reflection of the light 

 from the long spicula which are projected from it. 



The height of the sponge from the basal membrane on 

 which the bases of the skeleton spicula are fixed, to the 

 apex of the largest of them, does not exceed about a line. 

 I could not get a section of the sponge at right angles to 

 its base, but if we may judge by the length of the internal 

 defensive spicula, the height from the base to the dermal 

 surface would not exceed 1-1 50th of an inch. The second 

 specimen covered the surface of a small pebble for the space 

 of three fourths of an inch in length by half an inch in 

 breadth, and the sponge presented the appearance of a thin, 

 brown incrustation. The minute oscula, irregularly dis- 

 persed on its surface, were visible by the aid of a lens of 

 two inches focus. When a portion of the sponge was im- 

 mersed in Canada balsam, the dermal membrane was seen 

 to be abundantly furnished with tension spicula, sometimes 

 dispersed singly, but most frequently collected in fasciculi, 

 which were often congregated in radiating groups. The 

 inner margin of an osculum on this piece of the sponge was 

 well supplied with internal defensive spicula. 



The large spicula of the sponge serve the purpose of both 

 skeleton and external defensive spicula. They are projected 

 at nearly right angles from the basal membrane, and extend 

 far beyond the dermal surface ; among them, and imbedded 

 in the sarcode, I found one very stout, short, cylindrical 

 spiculum, but this 1 believe to be only an abnormal form of 

 the usual skeleton ones, which, with very rare exceptions, 

 are regularly acuate. 



The internal defensive spicula vary considerably in size ; 

 I measured one of the longest and one of the shortest of 



