254 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



well-marked variations, especially such as are found isolated from the 

 normal form, are worthy, not only of being placed on record, but also 

 of figuring in nomenclature. 



The desirability of these variations being noticed in our literature 

 is well illustrated by a reference to the specimen of Fistulana piercing 

 Mitra, recently described in our Proceedings. This was treated by us 

 all as a hitherto unknown occurrence, but it may be mentioned that 

 there is a specimen of Fistulana in the British Museum, collected so 

 long ago as the days of Eelcher, which has pierced in precisely the 

 same manner through a valve of one of the VeneridiB. 



The uses of the variations seen are but little known ; but as an 

 illustration of the utility of spines it may be stated that Francois ^ 

 noticed that Murex fortispina could open, and did, in fact, open the 

 valves of Area by means of the tooth-like process on the outer lip. 



Variation is as well-marked and as striking a fact in Palaeontology 

 as in Recent Zoology, but owing to the vastness of the subject I have 

 confined myself to-night to a very brief outline of some facts presented 

 by recent molluscs, and a few suggestions made relative thereto, one 

 or two points being specially dwelt on. 



I have not attempted, as I had at first proposed, to give full 

 references for every fact mentioned, or the following pages would 

 have in the main borne the aspect of a bookseller's catalogue ; it must, 

 however, be taken that the work is, as such work must be, a com- 

 pilation from the labours of others.^ 



Hybridism in the Mollusca seems to have been but little studied. 

 It has been noticed (in captivity) in Limncea. Hartman states ^ that in 

 Partula hybrids are common amongst some species and rare in others, 

 those observed being usually the offspring of proximate species. He 

 suggests that as Partula is hermaphrodite they may produce fertile 

 hybrids, and throws out the conjecture that it is possible that some 

 forms of the genus may have so arisen. The occurrence is also said to 

 have been observed between several Helices, Rumina decollata and 

 Helix, Pyramidula rotundata and Vitrea lucida, Clausilia papillaris 

 and Pupa cinerea, Littorina rudis and L. obtusata, L. rudis and 

 L. litorea. Furtado * collected in the Azores ten specimens of Vitrina, 

 and in every one the reproductive organs were lacking ; from this 

 and the appearance of the shell he suggested that they might be 

 hybrids, and he cites similar suggestions which had been thrown out 

 with regard to Buliminus and Zonites (Mi/alinia) from those islands. 

 In this connection we may also mention the statement ^ that the inter- 

 breeding of French and Algerian races of Rumina decollata is said to 

 have produced a new variety with a dentiform callosity in the aperture. 



1 Arch. Zool. Exper., vol. ix (1891), pp. 240-242. 



^ At the request of several members a number of references have now been added, 

 but no attempt has been made to render them complete. 



2 Bull. Mus. Comp. Zool., vol. ix, p. 173. 



* Ann. Nat. Hist., ser. v, vol. ix, p. 397. 



* Gassies : Journ. CouchyL, vol. ii, p. 356. 



