536 P. W. GAMBLE AND J. H. ASHWORTH. 



thirteen pairs of nephridia, in A. Grub ii of five pairs. The 

 characters derived from the setoe are even more inapplicable 

 here than in previous cases, since A. Grubii and A. ecau- 

 data are closely similar in this respect, except that we find 

 (with Mesnil) that a crotchet identical with those of the 

 neuropodia occurs temporarily in the notopodia of each of 

 the last six segments or so of A. ecaudata 10 mm. long 

 (P1.24, fig. 37). 



These considerations lead one to a fairly wide definition of 

 the genus as a whole. The absence of the otocysts in A. 

 Claparedii unfortunately prevents the presence of these 

 organs being recognised as of generic value, but undoubtedly 

 they are one of the most critical points. Before, however, 

 deciding what the limits of the genus should be, it is neces- 

 sary to discuss Branchiomaldane, a small hermaphrodite 

 form, the structure and development of which is partly known 

 from the work of Langerhans (1881) and Mesnil (1898). 

 This form (for specimens of which we are indebted to the kind- 

 ness of M. Mesnil) is 8 to 20 mm. long, and becomes mature 

 when of the latter dimensions. It lives in transparent 

 ''mucus" tubes attached to calcareous algse in the English 

 Channel, and also in the Canary Islands. The prostomium is 

 somewhat larger than that of specimens of Arenicola ecau- 

 data of the same size, but is similarly conical and provided 

 with two lateral groups of eye-spots. The peristomium is 

 achtetous (and next segment ?) ; the following segments, of 

 which there may be thirty-three to fifty- oue, bear notopodia 

 and neuropodia. The notopodial seto3 are intermediate be- 

 tween those of post-larval A. marina and A. ecaudata, 

 while the neuropodia! crotchets resemble those of A. marina 

 in every point. The distinctive character is found in the gills, 

 which only commence in the hinder region (segments 18 to 21), 

 and occur as simple or slightly bifurcated filaments up to the 

 pygidium, those of the central part of the branchial region 

 beino- larger and bearing more processes (four) than the re- 

 mainder, which are simple, bifid, or trifid. This character 

 is considered of generic value by Langerhans, and accord- 



