326 F. P. SMITH ON SOME BRITISH SPIDERS TAKEN IN 1908. 



the legs, the position of the eyes, and the height of the clypeus ; 

 but all these characters are variable, and intermediate forms are 

 commonly found. The epigynum appears to exhibit no well- 

 marked differential character. 



The significance of the terms " variety " and " sub-species " 

 as employed in this and previous papers may need a few words 

 of explanation. We find in the Araneidea numerous instances 

 where certain types cannot be satisfactorily disposed of by the 

 usual binomial system, and where the use of sub-specific and 

 varietal names is conducive to the proper appreciation of the 

 real relationship between the forms in question. Individual 

 specimens are, after all, the only really existent and tangible 

 objects, and as soon as one begins even to group individuals into 

 species one finds that hard-and-fast rules are well-nigh im- 

 possible, and that personal opinion must of necessity play an 

 important part in the matter. At the same time a very 

 methodical student must obviously base his work on some 

 system which he can follow, more or less, as his opinion dictates, 

 or as circumstances demand. This being so, it is visibly a great 

 convenience to his confreres if he definitely gives some idea of 

 the principle upon which he works instead of imposing upon 

 them the necessity for deducing his methods from his results. 

 In the employment of the terms " species," " sub-species," and 

 " variety," I am quite aware that the criteria for their differentia- 

 tion must of necessity be almost conventional : still we are 

 dealing with a complex group of animals, and can hardly expect 

 to classify them scientifically and satisfactorily by a simple rule- 

 of -thumb formula. 



In cases where two forms occur differing very slightly in 

 the primary sexual characters in one sex {e.g. Aranea cucurbitina 

 and A. opisthographa) or in the primary sexual characters of 

 one sex and the secondary of the other (e.g. Philodromus aureolus 

 and P. cesjnticolis), and especially where intermediate forms exist, 

 or where, at any rate, both forms are subject to considerable 

 variation, I am inclined to regard them as sub-species and 

 adopt a trinomial system of nomenclature. Several species 

 at present regarded as distinct (e.g. Erigone dentipalpis and 

 E. atra) could with just as much reason be classified as sub- 

 species. 



Where two types identical in sexual structure differ in size, 



