OF WASHINGTON. 349 



curate work. He took up the older classification of this group 

 and showed how it had undergone changes, giving the present 

 disposition of it by Simon and the reasons for his classification, 

 concluding with a general description of the distribution and 

 habits of these spiders. 



Dr. Gill asked if Simon had introduced more satisfactory char 

 acters for the separation of the families than the relative ones 

 formerly used, enumerating a number of characters hitherto com 

 monly employed by arachnologists and commenting on their 

 slight value fier se. 



Dr. Marx replied that we are very fortunate to find anything 

 at all to distinguish families in the Arachnida and allied groups, 

 illustrating the difficulties experienced by a reference to the class 

 ification of scorpions. He pointed out the distinguishing char 

 acters in the Territelariae, and stated that Mr. Simon is known to 

 be an acute and very close observer and that he has made use, in 

 his classification, of very many and often apparently irrelevant 

 characters, on which he has however built a most elaborate 

 system. 



Dr. Gill argued that it is a hindrance to the advance of science 

 to erect families in any case where it is so difficult to get good, 

 sufficient, and at the same time easily recognizable characters to 

 separate them. 



Dr. Marx wished to know where the distinction must be 

 drawn between sufficient and insufficient differences in the sepa 

 ration of families, and illustrated the great difficulties met at this 

 point by reference to various representative' species of different 

 families of Arachnids. 



Dr. Riley thoroughly agreed with Dr. Gill, in thinking that 

 families should not be erected unless suitable and important char 

 acters separating them can be pointed out, and while he was 

 willing to have the minutest, as well as relative characters used, 

 if need be, in the separation of species or even of genera, he was 

 convinced of the necessity of having substantial differences pres 

 ent in the separation of larger groups. 



Professor Riley also referred to the opening statement in Dr. 

 Marx's paper and said that he had long felt the need of just such 

 a complete typical collection as Dr. Marx referred to, and that 

 he had long been endeavoring to secure a collection of that char- 



