216 A MONOGRAPH OF THE 



be the occurrence of a few acerate spicula dispersed among 

 those from Raphyrus ; but when we take into consideration 

 the anatomical peculiarities and the external forms of the 

 two sponges, there is not a moment's hesitation required in 

 distinguishing between them. 



Mr. Hancock, of Newcastle-on-Tyne, has divided Dr. 

 Johnston's Halichondria celata into twelve species, nine of 

 which he has designated and described in the 'Annals and 

 Magazine of Natural History,' second series, vol. iii, p. 321, 

 but it does not appear to me that this division into species is 

 natural or justifiable, as they are founded purely on differences 

 in form, without any adequate variations in their structural 

 characters to support such a division. Nearly all these pro- 

 posed new species have the same habit and the same forms 

 of spicula, with only such an amount of variation in size 

 and form as may readily be found in a single field of view 

 beneath the microscope, in any well-known specimen of 

 Halichondria celata of Johnston when mounted in Canada 

 balsam. 



Since the publication of Mr. Hancock's paper I have 

 examined a large number of specimens from the North Sea 

 and various other localities, but I have failed entirely in 

 finding one which could not be readily and justly referred 

 to Dr. Johnston's second variety of the sponge, Cliona celata, 

 Grant. 



There are four of Mr. Hancock's species, C. gracilis, 

 Northumbrica, corallinoides, and vastifica, from which he 

 figures small acerate spicula as accompanying the spinulate 

 ones, but he does not say from what part of the sponge he 

 obtained them, nor what proportion they bore to the spi- 

 nulate ones ; but as adventitious spicula of various forms 

 are by no means uncommon on the surface of many sponges 

 in their natural state, and as they are frequently firmly 

 cemented on the dermal membrane in the same manner as 

 grains of sand and other extraneous matters are, I must at 

 present doubt their being the normal forms belonging to 

 Dr. Grant's Cliona celata, and especially as acerate forms 

 of spicula are so exceedingly abundant among the sandy 

 detritus of the sea bottom. There is no British sponge 



