1898] NOTES AND COMMENTS 297 



this is that these cells are evacuated apparently intact, not only 

 with their chlorophvl, but with the other substances that they 

 contain. 



4. It has been noticed that Helix hortensis produces the same 

 patterns on the lattice work of a wooden fence covered with PI euro- 

 coccus vulgaris. A figure of the pattern referred to will be found 

 reproduced in La Feuille des jevmes Naturalistes, September, from 

 which journal we take this note. 



Abnormal Shells of Plaxorbis 



The abnormalities of our fresh-water snails will be no new fact to 

 bring before the notice of our readers, but attention may well be 

 directed to a paper by Mr A. G. Stubbs on abnormal specimens of 

 Planorbis spirorbis from Tenby. The paper was read before the 

 Conchological Society, and is published in the October number of 

 their Journal. A good plate is provided, and the shells are seen to 

 be contorted in every direction, but mainly into that of a spiral, 

 some of these so much drawn out as to be nine or ten times the 

 height of the normal shell. Mr Stubbs accepts Mr J. W. Taylor's 

 explanation as to the cause of this curious distortion : — " that when 

 the water [in this ditch] is nearly dried up, the efforts of the crea- 

 tures in forcing their way through the thick mud in which they are 

 sometimes left partially embedded, to again reach the water, may 

 easily cause an alteration in the direction of a new shell growth, if at 

 the time in course of formation." 



A Remarkable Marine Organism 



Among a number of sponges from Eamesvaran Island, Gulf of 

 Manaar, sent to Dr Arthur Dendy for identification for the Madras 

 Museum, were some fifteen specimens of cushion-shaped masses of a 

 brown colour, from 13 mm. to 36 mm. in diameter, attached to 

 rock fragments. These masses are compact and tough in texture, 

 after preservation in spirit, like indiarubber, and there is a deal of 

 sand in the deeper layers. When cut in half vertically they show 

 strongly-marked, concentric lamellae, the effect of alternating bands 

 of fiocculent (opaque) and transparent layers. The opaque layers 

 are connected together by a coarse network of radially ramifying 

 strands. In the transparent layers are seen, after careful examina- 

 tion, innumerable exceedingly slender unbranched threads, which 

 prove to be the cellulose sheaths of chains of short, rod-like 

 bacteria. Dr Dendy thinks that there are two possible views as to 

 the nature of Pontobolbos, as he calls this remarkable structure, and 

 these are (1) that the organism is entirely bacterial in origin, the 



