BUFFALO SOCIETY OF NATURAL SCIENCES 239 



seriatim, bearing in mind that details in structure are in most cases 

 unavailable and that consequently genetic relationships are obscured. 

 Of the genus Stylonurus, three species have been described by Laurie: 

 S. elegans, S. macro phthalmus , and S. ornatus. The first species has 

 been placed by Clarke and Ruedemann into the subgenus Ctenop- 

 terus, together with S. cestrotus Clarke, and 5. multispinosus Clarke 

 and Ruedemann ; the former from the Shawangunk, the latter from 

 the Pittsford, the subgeneric characters being the relatively greater 

 length of the second and third pairs of legs when compared to the 

 first, and the presence on the former of more than two pairs of long, 

 slightly curved spines, which are vertical on the lower side of the 

 segments (Clarke and Ruedemann, 39, 286-287). The Scottish species 

 is so different from the two American forms grouped with it that the 

 author is tempted to take exception to their being placed in the same 

 subgenus, particularly because the very characteristics which are 

 mentioned as diagnostic are not always observable. My reasons for 

 objecting to the subgeneric grouping of this form under Ctenopterus 

 are as follows : (1) It is unsafe to base a taxonomic group of such great 

 value as a subgenus upon the characteristics of one set of organs 

 alone, as for instance, the legs. Nothing at all is known of the body 

 of S. multispinosus and very little about that of S. elegans; only that 

 of S. cestrotus having been found in good enough preservation to 

 allow of restoration. (2) Single identical morphological characters 

 do not of themselves establish specific relationship and, therefore a 

 fortiori they cannot be used to unite their possessors into groups of 

 higher taxonomic value for it is a law of palaeontology which is com- 

 ing more and more to be recognized, that the same morphological 

 characters crop out in many diverse phyletic groups and their pres- 

 ence in no wise indicates genetic relation. Thus, a modification in 

 the proportions of the legs or in the number of spines cannot be con- 

 sidered characters of subgeneric rank. (3) The length, breadth, 

 general form and grouping of the spines on the second aud third 

 pairs of legs are not at all similar in S. elegans and S. cestrotus (fig. 

 23). The comparatively short spines of about equal length, regu- 

 larly spaced, and projecting at almost right angles from the walking 

 legs, in S. excelsior (provided the restoration of this species is correct) 

 and in S. cestrotus, together with the greater length in the second and 

 third pairs of legs as compared with the first pair, might allow of these 

 two species being placed in the same subgenus, and with them quite 

 probably S. multispinosus. S. elegans, however, is too distinct, it 



