BUFFALO SOCIETY OF NATURAL SCIENCES 25 1 



offer many new illustrations of this law which is so simple, which so 

 strongly makes its appeal to the reason, and which yet is so con- 

 stantly ignored. The Carbonic species of Eurypterus develop spines 

 wherever possible; the surface scales are produced into pointed wedges 

 or spines; the ends of the epimera grow out to a great length; spines 

 develop on the appendages not only in rows along the various seg- 

 ments but also on the lines of junction between segments: showing 

 that the final expression of morphological characters in the eurypterids 

 was the development of spines which was followed by extinction. 

 Such a development has seemed expectable to many authors for the 

 species living in the late Palaeozoic, in the Mississippic, and Carbonic; 

 but there is really nothing to prevent these phylogerontic characters 

 from appearing much earlier. And so, to apply all of these general 

 statements to the case in question, I would say that the epimeral 

 spines observable on S. myops indicate that the line which that 

 species represented was on the decline even in the Siluric, at a time 

 when the majority of eurypterids were at their acme. A glance at 

 the illustration of 5. scoticus (Woodward 312, PI. XXII) will show to 

 the reader that this species has a typically gerontic appearance. Its 

 epimeral prolongations do not in the least resemble those in S. myops, 

 but are most like those of S. macrophthalmus from the Ludlow. 



Two points remain as supposedly indicative of relation between 

 these two species. The position of the eyes is, it seems to the author, 

 the only feature of marked similarity, but certain of the British 

 forms also show such a position, so that it is not of striking impor- 

 tance. As for the ornamentation of the tergites, I can see little to 

 warrant the statement that the sculpture is similar in the two species. 



The species Stylonurus (Tarsopterus) scoticus has now been com- 

 pared in detail with S. myops and it has been shown that they are not 

 closely related and consequently the presence of the first genus in 

 the Old Red sandstone not only does not militate against my thesis 

 that the faunas living in rivers coming from the same continent and 

 in the same latitude should be most alike, but it is actually an addi- 

 tional proof, for S. scoticus is most nearly related to Ludlow and Old 

 Red species, though it shows phylogerontic characteristics which 

 somewhat obscure its relations. 



The three remaining species of Stylonurus from the Old Red may 

 be quickly dismissed. S. symondsii, from England, is represented 

 by a single apparently complete carapace which is almost as long 

 as wide, but is distinctly narrower posteriorly than anteriorly. There 





