520 MR MALCOLM LAURIE ON THE 



Considering the presence of preoral chelicerse in Slimonia, Pterygotus, and Eurypterus, 

 I have little hesitation in supporting the latter view and regarding this chela as a preoral 

 appendage. 



I have been unable to ascertain anything new with regard to the other important 

 genera of Eurypterids : — Dolichopterus* Drepanopterus,\ and Glyptoscorpins.l With 

 regard to the last of these, I can add nothing to Mr Peach's admirable description, 

 and am happy to find myself in agreement with him on almost every point. I think 

 it is quite certain that many carboniferous forms are true Eurypteri ; § but that 

 Glyptoscorpius is a good genus, and perfectly distinct from Eurypterus, admits of 

 no doubt. Mr Peach suggests that it had eyes like those of Eurypterus Scouleri ; but, 

 if this be so, it is against its having any very near relationship with Scorpio, since 

 the lateral eyes in Scorpio are marginal in position. The combs and appendages seem to 

 relate it closely to Scorpio, and therefore, -according to my view, to separate it from the 

 Eurypteridas. 



Relations of the Eurypterids among themselves. 



The geological record is manifestly so incomplete as regards these forms — all the 

 important genera appearing practically simultaneously in the Upper Silurian, while frag- 

 ments of undetermined relationship occur as low down as the Moffat Shales — that no 

 deductions as to the phylogenetic relations of the various forms can be made from their 

 order of appearance. From a morphological standpoint, the family seems to fall into two 

 sections, determined chiefly by the position of the compound eyes. The first section, in 

 which the eyes are marginal, contains Pterygotus and Slimonia ; the rest of the genera 

 falling into the other section, with the eyes on the dorsal surface of the carapace. This 

 position of the eyes, however, while useful as a classificatory character, is not decisive as to 

 morphological grade. If, as seems probable, the Eurypterids are to be derived from such 

 forms as Olenellus, it would seem, at first sight, natural to take those forms which have 

 the eyes on the dorsal surface of the carapace as the more primitive, and to make 

 Eurypterus the starting-point for the whole series. It is quite possible, however, that 

 the free cheeks of the Trilobite correspond to the inturned portion of the carapace in 

 Eurypterids — the facial suture corresponding to the margin. In this case, the forms with 

 marginal eyes, such as Pterygotus, are the more primitive. A further argument in 

 favour of this point of view is that the lateral eyes in the Scorpionidse and Thely- 

 phonidse are marginal in position, and these forms must be derived from some way down 

 the Eurypterid stem. Other considerations appear to me to give greater probability to 

 the view that Pterygotus is the more primitive form. 



In the first place, the form of the body, with markedly differentiated tail segments, 



* Hall, loc. cit., 414. t Ladrie, loc. cit. t Peach, Trans. Roy. Soc. Edin., vol. xxx. 



§ Such forms as E. mansfieldi, E. rnazonensis, and E. stylus, from the carboniferous rocks of Pennsylvania (Hall, 

 Second Geol. Surv., Pennslyvania, vol. ppp), are undoubtedly true Eurypterids. E. Scabrosus (Woodward, Geol. May., 

 Dec. 3, vol. iv. p. 481) seems less certain, as the limbs are very different from the normal Eurypterid type. 



