250 THE HABITAT OF THE EURYPTERIDA 



margin is quite as likely to be curved as to be nearly flat (as in S. 

 scoticus). A comparison of the proportions of length to breadth of 

 carapace in these two species and in two others with which relation- 

 ship might more readily be established will, when taken in connection 

 with the illustrations, show that S. scoticus in so far as its carapace is 

 concerned, is far more nearly related to associated forms in the Old 

 Red and to others in the Ludlow, than to the Shawangunk forms. 



From these figures we may conclude that Clarke and Ruedemann 

 find the approximate ratio of length to breadth of carapace in S.myops 

 to be as 2 : 3, but it is evident that in S. scoticus it is 4 : 5. It is not to 

 be denied that the ratio changes from that in the young of S. myops 

 where it is 2 : 3 to that in the type where it is nearly 3 : 4, and perhaps 

 it might be conceded that in larger forms the ratio might approach 

 4:5; but we cannot be sure. There is in the Ludlow, however, a 

 species which has a carapace proportioned exactly as in S. scoticus 

 and even in the Old Red is a species, S. powriei, with proportions 

 almost the same. Thus there is no need to form conjectures about 

 what might be possible relations to a Middle Siluric species from 

 Appalachia when there are forms which actually show the similarity 

 in formations derived from the same land-mass. 



A second point of supposed similarity between S. scoticus and 5. 

 myops was the occurrence of long and pronounced epimera in both 

 species. I have in another part of this paper discussed the significance 

 of spinous prolongations on the epimera, but I shall call attention to 

 the arguments again, since they are not universally recognized. 

 Beecher has assembled a wealth of illustration from all branches of 

 the animal kingdom to show that the appearance of spines as a modifi- 

 cation of any morphological character marks degeneration in respect 

 to that character, and, when extreme spinosity is accompanied by 

 certain other easily recognizable and similarly degenerate characters 

 the species, genus or family, all members of which show like degener- 

 ation, is doomed to decline and extinction. But not only that; as 

 Beecher, Hyatt, and a few present-day palaeontologists, notably 

 Grabau, have shown and have demonstrated by countless illustra- 

 tions which have led to the most certain deductions, the formation of 

 spines is a homeomorphic character, not in the least indicative of 

 genetic relationship in forms which develop such spines, but marking 

 only an onto- or phylogenetic stage. Spines may and do appear in 

 end-members of totally distinct phyletic groups and are of absolutely 

 no diagnostic value in determining true relations. The Eurypteridae 



