240 



THE HABITAT OF THE EURYPTERIDA 



seems to me, to be considered even subgenerically related, while spe- 

 cifically this species must certainly stand alone. This is especially 

 evident when we consider (4) That one of the two diagnostic charac- 

 ters of the subgenus Ctenopterus depends upon the comparison of 

 the lengths of the first three pairs of legs, the particular comparison 



Fig. 23 



a. Stylonurus elegans Laurie. Second and third legs on right side. (After 

 Laurie, 1900, pi. II, fig. 12.) 



b. Stylonurus cestrotus Clarke. Second and third legs on left side. (After 

 Clarke and Ruedemann, 1912, pi. XLIX, fig. 4.) 



being made between the first, and the second and third pairs, but in 

 .5. elegans the first pair is unknown. 



Stylonurus ornatus and S. macro phthalmus are in some respects 

 quite closely related to species occurring in the later Scottish horizons 

 in connection with which they will be spoken of again. ' Here it is 

 sufficient to note that there are no North American species which 

 have the characters of the genus Stylonurus (sens, str.) namely, the 



