Palaeozoic Arachnida of North America. 21 



that "while the earUer euiypterids were marine and their dimacteric 

 fauna euryhahne; their later habit throughout the Devonic and 

 Carbonic led them final!}' into the fresh water." The species which 

 is most interesting inasmuch as it shows a close resemblance to 

 scorpions, is Eusarcus scoypionis from the Silurian (Bertie waterlime) 

 quanies at Williamsville and Buffalo. Yet it does not seem reason- 

 able to imagine that Eusarcus is an ancestor of scorpions, first because 

 of the differences in structure and development mentioned above, 

 and then because of the occurrence in the same waterlime of a true 

 Silurian scorpion, Proscorpius osborni, which must have led a marine 

 life. Of the European eurypterids none resembles scorpions more 

 than Slimonia acuminata, yet in this case the same objection holds 

 true and true scorpions were there already represented by Palaeo- 

 phonus. There remains then the only alternative that the Xiphosura, 

 Eurypterida and scorpions developed independently and that the 

 great similarity between such forms as Slimonia, Eusarcus and 

 scorpions is due to convergence, as Thorell has already suggested. 



The Haptopoda, Phalangiotarbi, Anthracomarti, Opihones and 

 Acari show some remarkable similarities in structure and may have 

 had another common ancestor, but no Acari are known to have 

 occured in the Palaeozoic era and there are no connecting links 

 between either of these orders and the trilobites. The pseudo- 

 scorpions are not known to occur in the Palaeozoic. They show 

 only external similarity to scorpions and their origin cannot be 

 traced. In the number of abdominal segments and in the arrange- 

 ment of the coxae they resemble rather the Pedipalpi, but it Would 

 be very hazardous to derive them from this group. The Solifugae 

 stand quite isolated. The Pedipalpi and Araneae have much in 

 common both in their external and internal organization, but their 

 origin is as dark as that of the preceding orders. 



Great activity in the production of new arachnid forms must 

 have taken place at the end of the Devonian or the beginning 

 of the Lower Carboniferous period, since, the Coal Measures 

 or Pennsylvanian show already the majority of orders in full de- 

 velopment. All these forms have undoubtedly the structure of 

 terrestrial arachnids, although it is not impossible that some Anthra- 

 comarti and Phalangiotarbi led an aquatic life similar to that of 

 recent hydrachnids among the Acari. Fritsch has pointed out that 

 on the bodies of two Bohemian species of Promygale, which genus 

 according to Pocock is synonymous with Anthracomortus, are found 

 parasitical gastropods, Spiroglyphus, whereas all other arachnids 

 from the same region are free from them. This argument, however. 



