SPINNING MOLLUSCS. 303 



freely extended into the water, and the mantle-edges expanded ; 

 when the vase was moved or otherwise shaken, the animal con- 

 tracted the mantle over its back, and descended " head foremost, 

 as it were dropping down to the bottom, leaving a mucous fila- 

 ment attached to the glass" ; subsequently, Gray adds, it ascended 

 by the filament, rising thus towards the surface, and becoming 

 attached to the glass as before.* 



Limapontihxe. 

 A supposed planarian-worm, Planaria variegata — probably a 

 Limapontia\ — was observed by Dalyell to be liable, in crawling 

 up the side of a vessel, to drop to the bottom, its descent being 

 apparently retarded, the observer says, by an invisible thread. J 



ASPIDOBRANCHIATA. 



In the whole of the Aspidobranchiata we have but a single 

 observation, and this, it is said, requires confirmation. It is not 

 surprising that no case of spinning occurs among the Limpet and 

 Limpet-like families ; but the absence of records for the land 

 operculates of the order — Helicina, &c. — is less easy to under- 

 stand, especially in view of the fact that several of the land 

 operculates regarded as Pectinibranchiata are known to suspend 

 themselves. The Aspidobranch said to be a spinner is our little 

 fresh-water nerite (Neritinafluviatilis), whose name appears in 

 this capacity in most of the books ; its only claim to notoriety in 

 this respect, however, rests upon the fact that it was listed by 

 Mr. Warington (with several air-breathing Water-Snails) as 

 having been observed by him to spin.§ No particulars are 

 given, and it is supposed by Mr. Tye that the observer may 

 have been mistaken. || 



* Gray, 'Annals and Magazine of Natural History' (3), iv. (1859), 

 pp. 239-40. 



f Johnston, ' Catalogue of the British Non-parasitical Worms in the 

 British Museum,' 1865, p. 12. 



I Dalyell, 'The Powers of the Creator displayed in the Creation,' ii. 

 (1853), pp. 115-6. 



§ Warington, 1854, I. c. 



|| Tye, 1874, I. c. ; 1878, L c. 



