90 



I have, therefore, merely drawn it to represent a peculiarity which 

 I have never met with in that or any other species. On reference to 

 the figure, there appears, as it were, a groove or division round the 

 circumference, similar to that formed by two cups when placed on 

 each other so as to make their rims or upper edges meet. There also 

 seems to be a peculiarity in the arrangement of the tentacula : — the 

 tentacula of Xanihidia generally pass from the body in a direction 

 perpendicular to its centre without any apparent fixed arrangement 

 of position, but in this instance an inspection of the figure will show 

 that both in the upper and lower portions there are two circlets of 

 tentacula, one placed round each extremity and another round that 

 part where the specimen appears to be separated. The size is ^4-jth 

 of an inch in diameter ; number of tentacula about 25. 



I now beg to call your attention to the following observations 

 upon recent Xanthidia, and this is I believe the only instance which 

 has been mentioned since Mr. White read his paper in February, 1842, 

 where he states that fig. 14, PI. VIII. Vol. i. of these Transactions, was a 

 representation of a Xanthidium which was received from New York 

 in some water sent to Mr. E. J. Quekett, by Professor Baily, but as I 

 had not the pleasure to see more than the specimen figured by 

 Mr. White, I have taken drawings of the several species which have 

 been brought under my observation by my friend Mr. J. T. Norman. 

 They were discovered in some Thames mud, taken up at Greenhithe, 

 in Kent, in July last : it consisted partly of the usual detritus of the 

 river, and a portion of that slimy description which is found upon piles 

 or stones which are covered by the water at certain states of the tide. 

 After this mud had been washed in the usual manner, the residuum was 

 treated with nitric and sulphuric acids and again washed. These 

 Xanihidia are evidently not of a siliceous nature, and it is therefore 

 remarkable that such powerful acids should not have destroyed them. 

 On referring to Mr. Deane's paper on those Xanihidia which he 

 found in chalk near Dover, I perceive he also states that they are 

 not siliceous. I consider them to be of a horny nature, similar to the 

 wiry-sponges, which Mr. Bowerbank describes as being very dffiicult 

 to destroy without the action of fire. 



These recent specimens I have arranged in the same order as laid 

 down in Mr. White's paper, but refrain, in the present state of my 

 enquiries, to assert that they are either new or identical with the fossil 

 specimens figured by him. 



I deem the discovery of these species so near to London a very 

 fortunate circumstance, as it will afford opportunity to those persons 



