311 



Staines Gasworks 

 comprise : — 



Vitrea crystalUna (Miill 



where some excavations were in progress. They 



V. nitidula (Drap.). 

 Zonitoidcs nitidiis (Miill.). 

 Pyramidula rotundata (Miill.). 

 Hygromia hispida (L.). 

 H. rufeseens (Peun.). 

 Vallonia pulchella (Miill.). 

 V. costata (Miill.). 

 V. excentrica, Sterki. 

 Helix nemoralis, L. 

 M. hortensis, Miill. 

 Coehlicopa lubrica (Miill.). 

 Jaminia muscornm (L.). 

 Vertigo pygmcea (Drap.). 

 V. antivertigo (Drap.). 

 Clausilia laminata (Mont.). 

 Succinea putris (L.). 

 S. elegans, Risso. 

 Carychium minimum, Miill. 

 Ancylus Jluviatilis, Miill. 

 Acroloxus IncHstris (L.). 

 Limncea auricularia (L.). 

 L. pereger (Miill.). 

 L. palustris (Miill.). 

 L. trnncatiila (Miill.). 



L. stagnalis (L.). 



Amphipeplea glutinosa (Mtill.). 



Planorbis cornetis (L.). 



P. albus, Miill. 



P. Stroemi, West. 



P. crista (L.). 



P. carinatits, Miill. 



P. icmbilicatus, Miill. 



P. vortex (L.). 



P. spirorbis (L.). 



P. eontortus (L.). 



P. fontanus (Lightfoot). 



Physa fontinalis (L.). 



Bithynia tentaculata (L.). 



B. Leachii (Sliepp.). 



Valvaia piscinalis (Miill .) . 



V. cristata, Mull. 

 Keritina Jluviatilis (L.). 

 Spheerium corneum (L.). 

 Pisidium mnnicum (Miill.). 

 P. Henslowianicm (Shepp.). 

 P. subtruncatiim, Malm. 

 P. pulchellum, Jenyns. 

 P. pusillum (Gmel.). 

 P. Gassiesimmm, Dupuy. 



The Pisidia, however, arc not fully worked out, so quite possibly the 

 remaining three British species are also represented. 



Several species found by Messrs. Kennard & Woodward did not 

 occur in this section ; the only two species additional to their list are 

 : Helix hortensis and Vallonia costata. Perhaps the most interesting find 

 was the one example of Amphipeplea glutinosa. J. E. Cooper. 



Note on the occurrence of Pearls in Haliotis gigantea and 

 Pegten sp. — Mr. R. Gordon Smith, wlio has recently returned from 

 a visit to Japan, has presented various interesting zoological collections 



j to the British Museum, and among them are the pearls now exhibited. 

 It is a well-known fact that pearls are produced by both Gastropods 



' and Bivalves, and that they occur more frequently in the latter. They 

 have already been recorded from the genera Strombus, Turbiiiella, Haliotis, 



* Margaritifera, Placuna, Malleus, Mytilus, Modiola, Pinna, Anomia, 

 Ostrea, Spondyhis, Area, Tridacna, Hippopus, Donax, Tellina, Unio, 

 and Anodonta, and there does not appear to be any special reason why 



1 other genera of Pelecypoda should not be pearl-producing if infested 

 by the larvae of Cestode and other worms. I now have to record the 

 occurrence of pearls in Haliotis gigantea and a species of Pecten. 



i Experiments with regard to the artificial production of pearls in Haliotis 

 have been made by M. Louis Boutan, but their actual natural occurrence 



■ in that genus has, I believe, only once been noted hitherto.' Some of 

 the Haliotis pearls brought home by Mr. Gordon Smith are of beautiful 

 lustre and very large, measuring as much as 24 millimetres (11 inch) in 

 length. They are often bean-shaped, and generally somewhat compressed. 

 They are found in the Haliotis gigantea ('Awabi' of the Japanese), and 



J. Keep : Xautilus, 1890, vol. iv, p. 15. 



