338 mr. albany hancock ox 



Shortly after the appearance of the paper above alluded to, I 

 satisfied myself that the larger bodies found in contact with the 

 surface of Cliona celata were not organically connected with it as 

 I originally thought, but were really nothing more than decalci- 

 fied portions of the horny membranous tissue of the oyster shell 

 within which the Cliona was buried, and sometime ago I wrote 

 to Dr. Bowerbank to this effect.* If, therefore, Cliona works 

 out the cavities it inhabits in the manner I supposed, namely, 

 mechanically, it must be by the aid of the smaller bodies de- 

 scribed in my paper, or by the spicula themselves. 



My object however is not, on the present occasion, to discuss 

 the means by which Cliona excavates its habitation, but rather 

 to give some additional specific characters that distinguish the 

 British species, and which originally escaped observation. But 

 in the first place it must be stated, that Dr. Bowerbank is not 

 exactly correct when he asserts, as he has done in the secoud 

 volume, p. 216, of his recently published "Monograph of the 

 British SpongiadaB," that I have divided Dr. Johnston's Hali- 

 chondria celata into twelve species. It does not appear that Dr. 

 Johnston ever saw any one of the species described by me : there 

 is certainly nothing in his description to show that he had ex- 

 amined more than one form of Cliona. \ Neither do I see any 

 reason for believing that Dr. Bowerbank bun self has enjoyed 

 any greater advantage ; for if he had had in his possession speci- 

 mens of my species, he assuredly would never have written that 

 "nearly all these proposed new species have the same habit and 

 the same forms of spicida, 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 Hali- 

 chondria celata of Johnston when mounted in Canada balsam. "J 



* On the 2Sth February, 1866. 



t This however does not appear to have been Dr. Johnston's own opinion. In a letter I 

 had the pleasure of receiving from that excellent naturalist, shortly after the publication of 

 my paper on Cliona, speaking on the subject, he says, " I have no doubt my C. celata em- 

 braces several species." But this was a hasty utterance written on the spur of the moment, 

 and probably meant nothing more than an expression of his conviction that there were 

 more than one species of British Cliona. 



t " Monograph of the British Spongiadse." Vol. II, p. 216. 



