SCIENCE-GOSSIP. 



J 35 



is, quite improperly and unfairly, ignored. This 

 method has at least the advantage that the 

 numerous fallacies and inaccuracies with which 

 it is beset are obvious on the face of it. By its 

 use one may especially trace a series of grada- 

 tions from full strength to absence in a series of 

 band-formulae, such as, for instance, the common 

 one in T. horteusis, of 12345, I -2345> I ^345. I0 345- 

 These results are tabulated by calculating the 

 average strength of one band : for instance in two 

 shells of the fairly common B. F. £2345, ten bands 

 are present and they have a strength of nine : 

 hence each band =09, which is in fact the average 

 strength of all the tumoralis bands considered. 

 Generally speaking the more often a band occurs, 

 the greater is its average strength : thus 3 is nearly 



the Old Red generally. Each hedge-bank almost 

 has a Tachca fauna with individual peculiarities well 

 marked : for instance, on a few yards of a bank 

 near Whitecross, Hereford, libellula (including the 

 unhanded form) markedly preponderates, while on 

 an adjoining length of the same bank, and within 

 a hundred yards, hardly anything except T. horteusis 

 vax.fasciata is to be found, though there is apparently 

 no difference in the lie of the two pieces, their vege- 

 tation, or other circumstances. Each small locality 

 seems to have its own at present inexplicable 

 peculiarities, and the characteristics of the De 

 Boinville shells may well arise from the fact 

 that I have not collected in just those small areas 

 which Mr. de Boinville chiefly affected— added to 

 our different mode of collecting. 



TaRLE III., SHOWING THE AVERAGE BAND STRENGTH OF THE VARIOUS BANDS IN THE COLOUR-FORMS 



of tachea nemoralis. the values are calculated to a degree of accuracy beyond 

 what the method of observation either requires or admits of. 



Locality : 





De Boinville. 



Moreton. 



Hunderton. 



Average 



T. nemoralis var. castanea. Band i 



0542 



No bands 



— 



0542 



2 



0-464 



i) 



0-250 



0-357 



3 



0639 



,, 



0-625 



632 



•i 



0493 



,. 



0250 



D'37 1 



5 



0500 



,, 



0250 



o'375 



e strength of all five bands 



0544 



,, 



0400 



0472 



T. ncmuiMis var. libellula. Band 1 



099 



0-768 



0650 



0739 



2 



0785 



0-892 



0-900 



0859 



3 



0904 



1 



I 



0968 



4 



0945 



0996 



0-954 



0965 



5 



0949 



0-992 



°'954 



0965 



Average strength of all five bands 



0905 



0935 



0900 



0913 



7". niraoralis vars. mista and rubella. Band 1 



772 



0723 



07S2 



0726 



2 



814 



0-922 



940 



0892 



3 



0841 



99s 



1 



0-946 



4 



0-909 



0994 



990 



0964 



5 



o-goG 



0982 



0-979 



0-956 



Average of all bands 



0-859 



0-930 



0-938 



0909 



All T. nemoralis. Hand 1 



0-821 



0738 



o'755 



0-771 



2 



0781 



0912 



0-905 



0-866 



3 



0845 



0-999 



0-9.11 



0'945 



4 



0887 



0995 



097S 



°'953 



5 



" -'■■!- 



0986 



..■,,.!., 



0946 





O854 



0927 



OglS 



0-900 



,,:;.„,.,, 



always the strongest, and the order is 3, 4, 5, 2, 1. 

 In all the tumoralii considered, however, the order 

 U 4. 5. 3. 2, 1 This is the result of theabnormali- 

 lies of the \>e Boinville shells, where the order is 

 5. 4, 3, 1. 2. In catfanta we find low vain. 

 average being less than 05. and the order 3, 1,5, 

 4,2 I-'or details see Table III. 



Speaking generally, it might be (aid that, though 

 mge of variation in Herefordshire is small, 

 some inteTotiri,; retail* rn.-i 

 expect 10 find that gi rotation hi 



constant influence in I the variations 



between the three stations on tli>: Old 



Braomy Hill 1. ball \-> •>■■>•■, mile acrost the 



Wye from the Hunderton locality, and about three 

 and a half from M 



le, as great as those !<■ ilnrlan and 



To be of value, this numerical method must be 

 widely used on some common plan, and the results 

 from all parts collated. It is, however, a laborious 

 and tedious task, and I am rather sceptical 

 whether sullicicnt data will ever be collected in this 

 way to make much headway with this, which is only 

 one of many problems of conchological variation. 



1 have said nothing about variation in band 

 formulae, size, weight, shape, etc., all of which 

 are still larger subjects than thi presenl As far 



is county is concerned, they will be tre I 



of in the paper on "Herefordshire Mollusca," whii li 



i-. in preparation for the Woolbopi 1 lub 1 may 



m thai Mr de Boinville alone has replied to 



the appeal for " sax kfals of the 1 • Bnail 1 ol 



the hedge hank " which I made last yeai 

 1 i>r Grange, Hereford; Augutt, 1^7. 



