206 



THE BRITISH NATURALIST. 



[October 



Three Swallows in One Nest. — Some Swallows built a nest 

 this year in the verandah of Bockleton Court, near Tenbury, in 

 Worcestershire. When one of the birds began to sit it was remarked 

 that two others were feeding her. As this went on during the whole 

 period of incubation, it was noticed over and over again, and there 

 could be no possible doubt about the fact. For aught I know this 

 may be a common occurrence, but it strikes me as being rather 

 curious, and I should much like to know whether a similar domestic 

 arrangement has often been observed. — F. E. Prescott-Decie, 

 14, Kensington Gate, London, W. 



How many Species are there of British Land and Fresh- 

 Water Mollusca ? — A reader of the "British Naturalist" has 

 written to ask the above question, and as it is one frequently put by 

 those just commencing to take an interest in the subject, I have 

 promised to reply somewhat fully. 



The fresh-water species are usually considered to number forty- 

 seven. To these some writers add four species of Hydvobia which 

 inhabit brackish water and Otina otis wmich is better placed among the 

 marine species. This raises the number to fifty-two. From this 

 number, besides the species just named, may be taken Anodon anatina, 

 perhaps a variety of A . cygnea, and Limnaea involuta, probably a variety 

 of L. peregva, as well as Physa acuta, which though a good species is 

 confined to warm water-tanks in one, or at most two localities. This 

 will reduce the number to forty-four. 



The smallest number to which the land species can be reduced is 

 seventy-nine, to these is generally added Testacella scutidum, now 

 regarded as a distinct species. The following three species have been 

 recently introduced, or at least recently discovered in this country, and 

 may possibly continue with us, Hyalina petronella, Helix elegans and 

 Pupa cinevea. Bulimus (Stenogyva) Goodallii and B. octona have about 

 the same claim to rank as British as Physa acuta, being confined to 

 hot-houses, into which they have been introduced with foreign 

 plants. 



The following species have been found once or more in the British 

 Islands, having been probably introduced by accident or design, Helix 

 villoso, H. lactea, H. personata, H. aperta, and Clausilia solida. Vertigo 

 lilljeborgi and V. tumida were formerly considered valid species, now 

 they are classed as varieties of other species. Limax tenellus is not 

 now known. Clausilia pavvula has been included in the list, small 

 examples of C. vugosa having been mistaken for this species. Succinea 

 puvvula, S. suecica, S. acuta, S. vitvca (a var. of S. putvis) and Helix 

 cantianiformis (a var. of H. cantiana) also appear on some lists. To 

 these may be added Helix lampra, a species manufactured out of H. 

 ericitovum by some continental conchologists. To these remain to be 



