JOURNAL OF CONCHOLOGY. 227 



possible that the irritation created by these creatures may have 

 been the cause of the Nautilus quitting its shell. If so, it tends 

 to show that the animal possesses the power of suddenly detach- 

 ing the shell-muscle from the shell. This is not surprising when 

 the feebleness of the scar and the fact that a thin transparent 

 membrane is secreted between the muscle and the scar upon 

 the shell are taken into consideration. The muscle evidently 

 has such a slight hold on the shell that a very small effort of 

 contraction would release it. If the theory be correct that the 

 Nautilus moves forward a certain space to form a fresh chamber, 

 relaxing its hold on the shell by the lateral muscles of attach- 

 ment, were there not some means of holding on there would be 

 considerable risk of the shell falling away from its inhabitant. 

 The siphon then, as suggested by Reeve, may be the means by 

 which the shell is held in position during that process. It might 

 be stretched the required length, or if moveable within the 

 siphonal tube it might be pulled forward the length of the 

 compartment, to be parted off by a new septum, and still leave 

 sufficient in the old siphonal tube to hold the shell from slipping 

 away. When the specimen observed by Mrs. Kenny quitted 

 its shell, it appears to have snapped the siphonal membrane, for 

 only about half an inch is still attached to the body. 



Abnormal Helix aspersa. — I was much surprised 

 when dissecting a specimen of Helix aspersa^ a few days ago, 

 to find that it was without a mandible, and had only an exceed- 

 ingly small portion of the lingual ribbon. Where the mandible 

 should have been there was a hard muscular band, about the 

 length of the mandible but much broader, giving the animal 

 the appearance of one with its mouth wide open. With the 

 exception of a very narrow strip of chitin, the floor of the 

 mouth was covered with the usual cartilaginous cushion, such 

 as the ribbon usually lies upon. The specimen was one which 

 I had had in confinement for some four years or so, and was 

 full-grown when I collected it. — W. E. Collinge, Leeds. 



