142 A renicolidae 



to the type specimen, as it is no longer in existence. The only 

 authoritative information regarding the species is that given in the 

 original account and figure. The embellishments added to the 

 diagnosis by some subsequent writers, without reference to the type, 

 are not admissible as evidence. 



The figure of A. branchialis given by Audouin and Edwards 

 represents an Arenicola with a short " tail;'' but with the characteristic 

 form of the ecaudate species, that is, the worm is only a little dilated 

 anteriorly. The writer has a number of specimens of A. grubii in 

 which, behind the last chaetiferous annulus, there is a region, 

 composed of three or four rings, about 6 nun. in length. The 

 corresponding region in Audouin and Edwards' specimen is drawn 

 about 9 mm. long. Their figure is almost certainly wrong in 

 representing this terminal portion as cylindrical. It should have 

 been conical. Making due allowance for this mistake, the figure 

 shows a specimen of such a character that, were it now in existence, 

 the writer has no doubt that it would be described as ecaudate, that 

 is, in contrast to species like A. marina, in which a well-developed 

 tail is present. 



Having reached the conclusion that the specimen of A. branchialis 

 was ecaudate, it may be stated at once that there is no reason to 

 associate A. branchialis with A. ccaudata, for there is no known 

 specimen of the latter with gills so far forward as the thirteenth, or 

 even the fourteenth, segment. The first pair of gills in A. ecaudata 

 is on the sixteenth segment, and, after examination of more 

 than two hundred specimens, the author is convinced that a forward 

 extension of the gills in this species, 1 so that they would correspond 

 in position to those of A. branchialis, never occurs. The first pair 

 of gills in A. grubii is normally on the twelfth segment, but not 

 infrequently the gills of this segment are wanting, and the thirteenth 

 is thus the first branchiate segment. The writer has seen more than 

 a dozen specimens of A. grvMi exhibiting this condition, and has one 

 specimen in which the thirteenth segment bears a gill on the left 

 side only. The fourteenth and succeeding segments are provided 

 with paired gills. This specimen agrees exactly, in the position of 

 its anterior gills, with that of A. branchialis figured by Audouin and 

 Edwards. It has been shown already that the " tail " of A. branchialis 

 is of the same nature as, and only slightly longer than, that present 



1 Only one specimen of A. ecaudata is known in which a forward extension 

 of the gills has occurred ; in this a small gill is present on the left side only of 

 the fifteenth segment. 



