Palaeozoic Arachnida of North America. 23 



Whether the scorpions of the late Palaeozoic Were already vivi- 

 parous or still laying eggs, and whether the male spiders had their 

 copulatory apparatus in the palp as is the case vnth recent spiders 

 and those from the amber, can be determined only when more 

 favorably preserved material is found. 



Comparison of the North American Upper Carboniferous Arachno- 

 logical Fauna with that of Europe and with the Recent Fauna. 



In comparing extinct Arachnida of one fauna with those of another 

 we must remember that the most important generic and specific 

 characters are often missing. To avoid unnecessary repetition 

 I shall give an illustration of the truth of this statement in the case 

 of the scorpions which by virtue of their size and the hardness of 

 their skeleton ought to present the least difficulties. One of the 

 most important not only specific, but generic characters is the 

 arrangement of the granules on the edge of the fingers of the pedi- 

 palp. None of the Carboniferous scorpions of Europe and North 

 America shows the slightest sign of these granules. Of course it 

 may be assumed that they did not have such granules, that the 

 granules are of more recent origin. But the similarity in other 

 characters makes such an assumption improbable. The very fact 

 that the pedipalp, bent in its normal position, presents the sides 

 of the fingers, is a sufficient cause to prevent us from seeing the 

 granules and would make it extremely difficult to obtain a mould 

 of them even in large recent forms. A character of great importance 

 in the systematics of recent scorpions is the presence of one or of 

 two spines in the articular membrane at the base of the last joint 

 of the legs. The recent family Scorpionidae has only one such 

 spine, while in the other five families there are at least two spines. 

 This character in recent forms is naturally combined with other 

 characters of importance, such as the shape of the sternum, the 

 structure of the comb and the number of side eyes. Anyone who 

 has had opportunity to study recent scorpions will agree with me 

 that the side eyes are visible only when the light falls on them under 

 a definite angle and cannot be distinguished from round granules 

 accompanying them when the light strikes them under another 

 angle It is nothing strange, then, that our knowledge of the side 

 eyes in Carboniferous scorpions is inaccurate and that this character 

 is not of great use. The sternum and the comb are sometimes 

 very well preserved, but in the great majority of cases the comb 

 is missing. To hope ever to find some of the finer specific cha- 

 racters such as the trichobothria, would be simply childish. What 



