PELAGIC LIFE, FALMOUTH. 213 



I found specimens of G-oniodoris castanea still abundant on 

 them ; but by the 28th of February there was only a single 

 individual left. On the 30th, while collecting in my praam I 

 was fortunate enough to see a specimen of Pleurobranchus 

 membranaceus swimming through the water. Mr. Grarstang (3) 

 says, referring to the curious method of propulsion this moUusk 

 adopts, as follows : — " When swimming freely the animal is 

 generally upon its back, but sometimes turns over either partially 

 or completely. It moves slowly forwards in this way, alternately 

 flapping, with wave-like contracticms, from before backwards, the 

 two halves of its broad foot. The mantle-flaps assist also in 

 this action." The specimen I had under observation for five 

 minutes seemed to me to expend a vast amount of energy and 

 to obtain nothing in return. It swam nearly around my praam, 

 and, seemingly having exhausted itself, sank slowly to the bottom 

 in three fathoms of water amid a forest of Zostera. So far as 

 I could see, the mollusk swam in the manner so accurately 

 described by my friend Mr. Grarstang. 



On the 7th of March, a single specimen of Dendronotus 

 arborescens was seen on the coal hulks. While collecting at 

 Helford on the 19th of that month, I was unable to find a 

 single specimen of uiEolis papillosa on the mud banks ; on the 

 other hand large specimens of Aplysia were fairly numerous. 



On the following day, while collecting in my praam under 

 the eastern breakwater, I noticed a specimen of Cyproea Europoea 

 hanging from one of the beams extending across that structure. 

 Close examination shewed that this mollusk was suspended from 

 the beam by a single thread of mucous, which was fixed to the 

 base of a large compound Ascidian ; the distance between the 

 mollusk and the beam being eleven and a quarter inches, and 

 from the head of the gasteropod to the sea six inches. This 

 mollusk weighed 0*4 grm. There was a fresh easterly wind 

 blowing at the time, accompanied by bright sunshine. 



Owing to the dryness of the atmosphere, I imagine the 

 gasteropod wished to moisten its gills with sea water, for it must 

 have been exposed to the air for at least an hour and a half 

 when I discovered it, hence I imagine this mucous film was 

 secreted. 



