450 v. W. UAMBLE AND J. H. ASHWORTH. 



semicircle (fig, 25). Each bears about five small but clearly 

 marked and nearly uniform teeth and a minute process 

 (figs. 24, 25). The chsetaB are slender, and never attain a 

 very great size, '4 mm. (in a specimen 100 mm. long) being 

 the extreme length attained in any of our specimens. 



A. cristata. — The crotchets of this species, especially of 

 young specimens, are very similar to those of A. marina, 

 except that the distal end is broader and more curved on the 

 side opposite the rostrum. Full-gi*own chsetae from a young 

 specimen 47*5 mm. in length are '2 mm. to '3 mm. long. 

 Each bears five or six teeth, the first of which (the one 

 nearest the rostrum) is the largest, the others gradually 

 decreasing in size (fig. 15). The same change in the angle 

 of the rostrum is also seen in this species as the specimens 

 increase in size. The rostrum of the chaeta described above 

 makes an angle of about 110° with the shaft. Fig. 16 

 represents a seta from a specimen 120 mm. long, in which 

 there are faint indications of three or four teeth, and the 

 rostrum makes an angle of about 130° with the shaft. An 

 unworn chseta from a very large specimen (300 mm. long) is 

 represented in fig. 17. The chseta bears two very small 

 teeth and a very minute process. This rostrum and the shaft 

 are nearly in a straight line, the angle between the two 

 being about 150°. The chtetse of this species are very long, 

 the full-gi'own ones of the large American specimen (360 mm. 

 long) reaching '9 mm. in length. The teeth being so small 

 are very early worn away, so that if the chsetse have been in 

 use they are entirely devoid of teeth, and then closely 

 resemble those of the large Laminarian specimens of A. 

 marina, the only characters distinguishing the two being 

 the curvature of the back of the chseta of A. cristata 

 (cf. figs. 9, 17). 



A. ecaudata and A. Grubii. — The neuropodial crotchets, 

 like the notopodial setse, of these two species are so closely 

 similar that no constant point of difference can be detected. 

 The shaft of each crotchet bears a moderately long rostrum, 

 tapering somewhat towards its point, behind which are two 



