EURYPTERID REMAINS FROM THE PENTLAND HJLLS. 577 



from the anterior border is a double depression, which I take to mark the position of 

 the median eyes. If they corresponded in size to these depressions they must have 

 been very large. Their position far forward on the carapace corresponds to what is 

 found in P. nuncius and Proscorpius osborni (Whitfield). In the middle line behind 

 the eyes and some 3 mm. from the anterior margin is a small depression, the significance 

 of which is unknown to me. There is a slight roughness at the left anterior corner of 

 the carapace, which probably marks the position of the lateral eyes. 



The six mesosomatic segments are wider than the carapace, i.e., about 11 mm., 

 but the lateral boundaries of this part of the body are very indistinct. In striking 

 contrast to the length of the carapace is the shortness of these segments. The first 

 measures only 2 mm., the next two 3 mm. each, and the remaining ones 4 mm. They 

 are thus considerably shorter and wider than the corresponding sclerites in P. nuncius. 

 Some obscure markings occur on them and seem to have some meaning. 



The first segment is cut across at the corners by the basal joints of the last pair of 

 legs. On the fifth segment is clearly seen a curved ridge cutting off the anterior right- 

 hand corner. Indications of a similar structure are visible on the three preceding seg- 

 ments. That on segment two, one may take as the impression of the outline of the 

 pectines. but the succeeding segments in recent scorpions bear no free appendages, but 

 only the respiratory organs or " lung books." If this curved ridge is an indication, as 

 I think probable, of the breathing organs, they must have been of a very different type 

 to those in the modern Scorpions. The lung books are generally regarded as modifica- 

 tions of plate-like appendages, bearing gill lamellae on their posterior surface. It does 

 not follow that because this form agrees with the recent ones in respect of the body 

 form and the arrangement of the prosomatic appendages that it had reached the same 

 point of specialisation in respect of its respiratory organs. The terrestrial mode of life 

 and consequent adaptation to air breathing may have come later. It is thus just pos- 

 sible that this curved ridge on the mesosomatic segments is the outline of a plate-like 

 gill bearing appendage. It is interesting to compare this structure with fig. la, which 

 is a reproduction of a figure of an embryo Scorpio fulvipes, published some years since 

 (5). The mesosomatic segments in this are seen to be marked with a curved 

 ridge corresponding more or less closely to that in P. loiidonensis. At the time, I 

 regarded this ridge as indicating the line of fusion of the edge of the abdominal ap- 

 pendage with the body, and I see no reason to change my view. 



The first metasomatic segment is as usual a truncated cone. The breadth at the 

 posterior margin is just equal to the length, i.e., 4 '5 mm. This segment is marked off 

 from the sixth, as the sixth is from the fifth, by a well-defined ridge. This ridge marks 

 the overlap of the two sclerites. The last five segments are even more obscure than 

 the rest of the specimen. The tail, which they constitute, appears to have been narrow 

 (2*5 mm.) and long, though the few segments remaining vary so much in length that 

 it is difficult to estimate the length of the whole. The first segment (No. 8 of the body) 

 measures 4 mm. in length, the next 6 mm. Beyond this the tail can be traced for 



