F. P. SMITH ON THE SPIDERS OF THE SUB-FAMILY ERIGONINAE. 17 



to suggest using such characters for a preliminary broad division 

 as will separate these hypothetical lines of development. The 

 difficulty becomes at once apparent when one considers that there 

 are still in existence very many of the more primitive types, and 

 the exact point at which the dividing line should be drawn 

 becomes more or less a matter of speculation. As a natural 

 consequence, the two sub-families thus formed, which I propose 

 to term Linyphiinae and Erigoninae, might reasonably be re- 

 garded as somewhat conventional and ill-defined; but when one 

 comprehends the vagueness of the boundaries which separate, 

 for example, the Drassidae from the Clubionidae, the Sparassidae 

 from the Philodromidae, or even the Agelenidae from the 

 Pisauridae, it becomes at once evident that it is often absolutely 

 necessary to employ minute and obscure structural details, and 

 even a concensus of characteristics, in order to reduce certain 

 motley assemblages of spiders into groups possessed at any rate 

 of something like homogeneity. 



Perhaps I might be permitted to draw for a moment upon 

 my imagination, and to sketch a purely hypothetical spider which 

 might reasonably be supposed to have enjoyed the distinction 

 of having been the ancestral type of the numerous species of 

 Linyphiidae. 



The thorax would be normal, the eyes arranged somewhat as 

 in Pachygnatha. The falces would be fairly powerful, each being 

 provided with a rudimentary stridulating organ. The legs would 

 be similar to those of Pachygnatha, but upon the tibia of each 

 one would appear a tiny spine. From such a creature let us 

 examine the process of evolution in the case of the Linyphiinae. 

 From the very first a tendency to develop additional spines upon 

 the legs becomes apparent, and continues with few exceptions 

 throughout the whole series. The palpal organs of the male 

 become vastly more complex as we advance, and the external 

 branch of the tarsus assumes a variety of forms, such as would 

 lead one to suppose that it fulfils some important function in 

 connection with the reproductive mechanism. The genital 

 aperture of the female in the higher forms usually possesses a 

 clavus, which often attains a high state of development. The 



Journ. Q. M. 0., Series II. — No. 54. 2 



