628 FRESH-WATER BIOLOGY 



20 (13) Certain dorsal spines of much greater length than others. ... 21 



All species in this group thus far reported from North America have large bifurcate spines. 

 A number of European species have simple spines without a lateral point near the tip. Griin- 

 spann classes the next species among the latter despite Stokes' positive statement that the 

 spines are bifurcate. 



21 (26) Head and neck free from covering of small spines. Large spines on 

 body proper 22 



22 (23) Large dorsal spines in longitudinal rows and of approximately equal 

 length. . Chaetonotus octonarius Stokes 1887. 



Length 0.0862 to 0.1034 mr n. Breadth of distinctly five-lobed head 

 0.0206 mm. Large spines unequally furcate arranged in two lateral 

 rows of three spines each and a median row with one anterior and one 

 posterior spine. The figures and descriptions given by Stokes and 

 Griinspann do not agree fully and may belong to separate species. 

 Rare; Trenton, New Jersey. 



FlG. 973. Chaetonotus octonarius in dorsal view. X about 580. (After Stokes.) 



23 (22) Large dorsal spines in two distinct transverse rows, with spines in 



one row clearly longer than those of the other 24 



24 (25) Eight (rarely fewer) large spines in two transverse rows set close 



together Chaetonotus longispinosus Stokes 1887. 



Length 0.0736 mm. Large spines usually eight, four in each row, or 

 five in one and three in the other; sometimes only four spines in all 

 (the others lost?); longer spines in posterior row. The figure in 

 Griinspann is really the next species. The European form identified 

 as this species is twice as large. Trenton, New Jersey. 



FIG. 974. Chaetonotus longispinosus in dorsal view. X 610. (After Stokes.) 



