SOME AQUATIC WORMS, ETC. I9I 



are unequally branched, and placed in two lateral lon- 

 gitudinal rows of three spines each, with one anterior 

 and one posterior central thorn. It seems to be the 

 least common of the species. 



9. Ch^t6notus spin6sulus (Fig. 142). 



The back usually bears seven unequally furcate 

 spines in two transverse rows — four spines in the an- 

 terior series, three in the posterior. Occasionally the 

 lateral thorns in the posterior row are suppressed, and 

 in some individuals the front series contains but three. 

 The lateral body-margins are bordered by short, con- 

 ical set^, which are constant in all the specimens thus 

 far observed. The rest of the upper surface is with- 

 out appendages of any kind, except the four tactile 

 vertical bristles present in all species. The egg is his- 

 pid with short hairs. 



10. Ch^t6notus longispin6sus (Fig. 143). 



The spines vary from four to eight, the latter being 

 the usual complement. They are nearly one-half the 

 length of the body, and curve upward and backward 

 in a wide arch from the center of the back. In front 

 of the anterior row the surface is setose with stiff, re- 

 curved bristles, and the body-margins are fringed by 

 coarse, rigid setae. The dorsal spines are always in 

 two transverse rows, but the number varies from four 

 in each to three in one and five in the other. They 

 are unequally furcate. 



4. Lepidod^rma rhomboides (Fig. 144V 



This is easily recognizable by the peculiar head, the 

 minute rhombic scales" covering the back and sides. 



