CATALOGUE OF THE MOLLUSC A OF SUSSEX. 177 



Testacella is a Lusitanian genus represented in Sussex by 

 two species — T. haliotidea and T. scutulum ; but as in both the 

 records appear to be in connection with cultivated ground, they 

 may possibly be modern introductions. The latter was brought 

 to Chichester thirty-four years ago. 



Methods of Dispersal. 



The molluscan fauna of the so-called "dew ponds" on the 

 South Downs has been investigated by Mr. Clement Eeid, who 

 contributed, in 1892, a most interesting paper "On the Natural 

 History of Isolated Ponds " to the fifth volume of the ' Trans- 

 actions of the Norfolk and Norwich Natural History Society.' 



These ponds are depressions puddled with clay, and used by 

 farmers as water reservoirs ; they are maintained by mist, fog, 

 and rain, the dew supply being quite inconsiderable. They 

 usually teem with animal life. Mr. Eeid observes that "they 

 are distant two or three miles from the nearest stream or marsh ; 

 and as the Downs rise to 800 ft., and the average height is fully 

 200 ft. above the highest streams, it follows that any aquatic 

 animals or plants found in the ponds must have been transported 

 uphill, as well as across uncongenial tracts of dry grass." 

 Limncea pereger is of common occurrence in these ponds. In the 

 summer of 1891 the writer noted that the pond near Chancton- 

 bury King was teeming with them. 



Mr. Reid alludes to "Ked Lion Pond on the open Down, three 

 miles south-east of Lewes ; height 540 ft. above the sea, and 

 530 ft. above the marshes of the Ouse ; nearest water, the 

 marshes of the Ouse, distant seven furlongs." In June, 1890, 

 he observed L. pereger in it. He also remarks that in a " small 

 pond by the side of the high road, half a mile west of Christ 

 Church, Stansted (near the Hampshire border), height 312 ft. 

 above the sea, and 220 ft. above the nearest stream," he noted 

 L. pereger and Planorbis spirorbis on September 25th, 1891. 

 Other species occurring in " dew ponds " are Limncea truncatula, 

 L. stagnalis, Planorbis vortex, Physa fontinalis, Pisidium pusillum 

 (occasionally), and Sphcerium corneum. 



The ancestors of these Molluscs were in all probability carried 

 up to the ponds on the feet of birds, or on large water insects. 

 Mr. Chapman records in the 'Field' (1884) that he shot a Snipe 



Zool. 4th ser. vol. XIX., Mmj, 1915. p 



