418 THE OPISTHOBRANCHIATE 



C. NOTASPIDEA. 

 i'amtZi/— PLEUEOBRANCHID^. 

 5. OscANius, Leach. 

 6. OscANius MEMBRANACEUs, Montagu. 



Examples of this species have been occasioually brought to us by 

 fishermen from the refuse of the beam trawl, but have been 

 obtained very rarely in the Sound. A very large specimen was 

 caught in a drift-net in 5 or 6 fathoms water off Jennycliff on 

 January 24th this year, and another large one was trawled in the 

 Sound exactly a month later. A few others had been taken in 

 previous years. 



The habits of congregation and migration of this species, as of 

 other Opisthobranchs, are worthy of notice, and 1 add here therefore 

 some observations made by other naturalists on the Devon and 

 Cornish coasts. 



Clark states,^ " These animals are frequently met with in the 

 coralline zone in summer, and in the winter are often washed ashore 

 on the Warren sands at Exmouth in considerable numbers." 



At Falmouth, thirty years ago, Cocks^ found the species rare at 

 Gwyllyn Vase under stones, and not uncommon in the Helford 

 River. 



At Torbay, according to Mr. A. R. Hunt,^ ''in December, 1873, 

 and January, 1874, Pleurohranchus {Oscanius) memhranaceus was 

 very abundant in the bay.'^ On February 7th Mr. Hunt took a 

 large specimen with a landing-net " at the back of the new pier, 

 floating about four feet below the surface." Immediately after- 

 wards rough weather came on, and for more than four years Mr. 

 Hunt saw only one specimen in Torbay. " The species was swept 

 out of the bay, and probably driven on shore." 



The broad foot {" pedal disc ") of this species serves for swimming 

 as well as for creeping. 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 contractions from before backwards, the two 

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

 This power of swimming explains the capture of one of our speci- 

 mens in a drift-net, as it does also of one of Mr. Hunt's with an 

 ordinary landing-net. 



» Clark, loc. cit., p. 269. 



2 Cocks, Contributions to the Fauna of Falmouth, Trans. Cornwall Polytech. See, 1849. 



3 Hunt, Notes on Torbay, Trans. Devon. Assoc, vol. x, 1878, pp. 189, 190. 



