ANATOMY AND CLASSIFICATION OP THE AUENICOLID.1^. 445 



than in any other species of Arenicola (see figs. 13, 14). 

 In the notopodia of A. cristata the capiHary setas appear to 

 be arranged in two more or less distinct transverse rows. 

 This is more obvious in the American than in the Neapolitan 

 specimens in our collection. The anterior row contains 

 shorter set^e than the posterior row, those in the former being 

 about two thirds the length of those in the latter (see PI. 24, 

 fig. 33), but in other characters they are identical. 



The seta3 of A. Claparedii are closely similar to those of 

 A. marina, but are rather smaller and their barbs more 

 obvious (fig. 23). 



The notopodial seta3 of A. ecaudata and A. Grubii are 

 identical in form and characters. They are more slender than 

 those of the three species named above, and taper very 

 gradually indeed to a long and slender tip. The haiiy pro- 

 cesses are fewer in number, smaller in size, and more closely 

 appressed to the shaft of the seta, so that they are much less 

 obvious than those of the setfe of the three caudate species 

 (fig. 20). 



The length of the largest notopodial setas we have met 

 with in the different species is as follows : — A. marina (250 

 mm. long) 7*5 mm., A. Claparedii (95 mm. long) 2*7 mm., 

 A. cristata (360 mm. long) 9 mm. (the shorter setje of the 

 anterior row are 6'4 mm. long in this specimen), A. ecaudata 

 and A. Grrubii (200 mm. long) 3"8 mm. 



The notopodial setae of post-larval stages of A. marina 

 show several interesting points. The notopodia of a specimen 

 of A. marina, 3*9 mm. long, bear from four to six setae, 

 which, on further examination, prove to be of two different 

 kinds (PI. 23, fig. 12). Some are typical capillary setae, 

 about '3 mm. long, bearing on their distal fourth minute 

 hairy processes similar to, but of course smaller than, those of 

 the adult setae (fig. 12 a). 



The other notopodial setfe are quite different, being only 

 about '17 ram. long, and ending in an exceedingly long fine 

 point. A little beyond the middle of its length the seta 

 bears a thin lamina or wing on each side, upon which very 



